I searched the forums but to my surprise I could not find any comments about the type and grade of battery for the RX8.
I have 3 year old OEM battery in my 2004 RX8 AT, and it is struggling to turn the engine over here in the cold North East (18F outside right now).

I chsrged it overnight, but it still was drawing 1-2 amps after 15 hours, so I assume the battery has had it.
Question is, what battery to replace it with - any suggestions ?

Thanks in advance

I don't have a lot of experience with such cold weather but I would imagine something with lots of cranking power.

Have you looked into optima red top?

I have a yellow top because of my car stereo upgrade but that weather you deal with is a whole different ball game. Good Luck

Yeah, from what I hear and read, Optima batteries are pretty damn good. Personally, I'm a fan of Interstate batteries. I've had one now for about 1.5-2 years and never a problem...matter of fact it was like 19 this a.m., car started up like a champ...no problem at all.

get the battery with the highest cranking power that fits snug inside the oem battery box and has the right terminals ..... simple

... that fits snug inside the oem battery box... simple

Snug, but still leaving the required air flow space, per the TSB that I linked in the other ongoing "What's the best battery" thread. Heat is a big killer of batteries. It's hot under the RX-8's hood, and the box is designed to allow cooling air flow.

I recommend getting a maintenance free battery. Something I have not been doing for my other cars, since I'm a cheapskate, but I do have a garage and a place to keep a jug of distilled water. And the other cars do not have their batteries buried under covers.

Ken

I've always found the Interstate line to be solid as well. My '05 came with an Interstate (the 'cranks but won't start' starter/battery upgrade TSB).

Mine is still good at present, but I may consider the Optima next year as it hits the four year old+ mark.

Max cold cranking amps in the existing box form factor is good advice.

Yeah, from what I hear and read, Optima batteries are pretty damn good. Personally, I'm a fan of Interstate batteries. I've had one now for about 1.5-2 years and never a problem...matter of fact it was like 19 this a.m., car started up like a champ...no problem at all.

i've used optima yellow tops and have had excellent results with them. the red top would be just fine if you are not needing a deep cycle battery.

what's the advantage of a deep cycle battery? accessories/stereo equipment?

w/ either optima red or yellow tops, is it a direct drop in replacement or do you need to make modifications?

deep cycle is for running bit stereos etc. It can take the abuse of being drained down and recharged better then standard batteries.

as for which one fits, here's a thread for the red tops http://www.rx8club.com/showthread.php?t=151027&highlight=optima

Red Top for RX-8:

http://store.summitracing.com/partdetail.asp?autofilter=1&part=ULT%2D9020%2D164&N=700+400089+306984+4294907824+4294881150+115&autoview=sku

Up until recently I have recommended Optima Yellow top. I consider deep-cycle capability important in this car, even in stock form. It does consume considerable dark current, which will run a battery down in just a few weeks. That will weaken an ordinary battery, even when charged back up. From what I've read, a deep discharge will reduce capacity of an ordinary battery about 25%. Also, deep-cycle do better in a flood-recovery scenario because they maintain voltage further into the discharge.

But, I have read on a few Electric Vehicle threads, some complaints about recent Optima Yellow Top and Blue Top batteries (essentially the same batteries with different posts). The folks who DIY electric car conversions live and die by their battery choices. According to those posts, Optima was taken over by Johnson Controls and the quality suffered. I don't have any first hand knowledge of this; my 3 1/2 year old Optima Yellow Top is doing great. But were I to buy a deep-cycle AGM battery today I might consider the Oddysey brand, which still gets high praise from the EV crowd.

For my money, an AGM battery is always the way to go. Absolutely no mess or maintenance, next to no venting in normal service, and won't leak even if you shoot a bullet into it.

+1 on the dimensions; don't give up cooling for a slightly larger battery. IMO, you're better off getting a top-quality battery that fits per the TSB.

Yellow Top for the RX-8:

http://store.summitracing.com/partdetail.asp?autofilter=1&part=ULT%2D9040%2D218&N=700+4294846476+4294907824+4294881150+115&autoview=sku

$189.95!! For that kind of money you can buy three regular batteries without even shopping for a bargain. Is it going to last three times as long?

Ken

yes, mine will last 3 times longer then a standard battery. There NO WAY a regular battery could withstand my stereo system.

$189.95!! For that kind of money you can buy three regular batteries without even shopping for a bargain. Is it going to last three times as long?

Ken

Check prices; you might have a problem finding a decent battery for $60 these days. The Interstate Battery cold-weather recommendation runs over $135 -- for a "flooded" type battery. Their "Standard" class 35 battery is still over $120. Even their el-cheapo offering is over $100.

So, not 3 times as expensive; more like 50 percent. Will a deep-cycle last 50 percent longer? Imo, it could but that doesn't even matter. I'll probably replace mine at 4 years whether it needs it or not. More important to me that it be trouble-free, I never have to deal with corrosion or maintenance, that it has some guts to get me out a flooded situation, and won't weaken appreciably if deep-discharged. A cheap flooded-type battery might sound like a bargain, but how much does it cost to replace cables and terminals due to corrosion? How much for a tow? For a few more bucks per year I like the peace of mind and total lack of hassles.

Yikes! Looks like I've been buying cheap batteries too long. The current battery in my Accord was something like $50 from Advance Auto. About five years ago the Honda dealer told me I needed a new battery, and recommended I go elsewhere because they charged $90 and the service manager thought that was outrageous. ($70 battery I bought then from Merchant's lasted a bit over 4 years.)

I better steel myself for today's (or tomorrow's) prices when Zoomy's battery needs replacement.

Ken

FWIW:

"Optima RedTop Starting 12 volt batteries, featuring Spiralcell technology, are designed for all of your starting needs. Vibration and jarring, whether from off-road use or major potholes, can kill a traditional battery. The tightly wound construction in Optima batteries minimizes the plate movement and subsequent damage caused by harsh conditions, extending battery life. These Optima RedTop batteries are leakproof, so they can be mounted anyplace inside a vehicle, in almost any position."

edit: oh, and the Red Top has over 900 cold cranking amps. Very nice for colder climes (and just in case you have to do a longer than normal de-flood start - not that that would ever happen. ;)

BRRRWWWARRRR !

Red Top user itz Here ~

Good Battery, a bit expensive. but its not very hard to find good deals online.

I can probably get a Red Top for around 150-160 shipped. :)

Oh for ur reference, I left my 8 For almost 2 weeks already. b4 I left NYC, I checked the battery's voltage. when I go back I will check it again, just to see how good optima battery is :)

Volts don't generally drop off; it's the capacity that dwindles (amp hours).

BRRRWWWARRRR !

Red Top user itz Here ~

Good Battery, a bit expensive. but its not very hard to find good deals online.

I can probably get a Red Top for around 150-160 shipped. :)

Oh for ur reference, I left my 8 For almost 2 weeks already. b4 I left NYC, I checked the battery's voltage. when I go back I will check it again, just to see how good optima battery is :)

Anyone tried a 34/78 Optima RedTop? Specs are

RedTop®; Battery; UNBOXED; Group 34/78; Cold Crank Amps 800; Crank Amps 1000; Reserve Capacity 100; Ampere Hour 50; Dual Terminal; L-10 in.; W-6 7/8 in.; H-7 13/16 in.;

The 35 specs are

RedTop®; Battery; UNBOXED; Group 35; Cold Crank Amps 720; Crank Amps 910; Reserve Capacity 90; Ampere Hour 44; Top Terminal; L-9 5/16 in.; W-6 3/4 in.; H-7 5/8 in.;

So the 34/78 is smaller with more juice. Question of fit I guess - and airflow around.

I ask because a friend has one that he can't use and is looking to get rid of cheap.

^ smaller would of course work although might require some shimming to preclude it rattling about. Of course make sure the red/black terminals are in the proper orientation so you don't require add'l extender cables.

Anyone tried a 34/78 Optima RedTop? Specs are

RedTop®; Battery; UNBOXED; Group 34/78; Cold Crank Amps 800; Crank Amps 1000; Reserve Capacity 100; Ampere Hour 50; Dual Terminal; L-10 in.; W-6 7/8 in.; H-7 13/16 in.;

The 35 specs are

RedTop®; Battery; UNBOXED; Group 35; Cold Crank Amps 720; Crank Amps 910; Reserve Capacity 90; Ampere Hour 44; Top Terminal; L-9 5/16 in.; W-6 3/4 in.; H-7 5/8 in.;

So the 34/78 is smaller with more juice. Question of fit I guess - and airflow around.

I ask because a friend has one that he can't use and is looking to get rid of cheap.

I'd stay with a Group 35, the battery box is designed to allow external air to circulate and cool the battery. The group34/78 is a bit long and will crowd the box. And I'm not sure if the terminals are oriented properly, you'd need to check.

If you'd like a Group35 with even better specs than either of the above, the Sears DieHard Platinum P-5 Group 35 has a 59 amp-hour capacity. It's has the same AGM benefits, has deep-cycle capability and a great warranty.

If you get one of the Optimas, make sure you also get the spacer that's supposed to come with it. The Optimas run short, and the spacer is needed to raise them to the correct height for the stock connectors.

Get a battery with a lifetime warranty. You'll never buy another battery again.

Thanks guys. Good to see you are still around Nubo. I don't get on here often enough myself.

Yep, that's 'cause the P-5 is an Odyssey OEM. Can't go wrong.

... If you'd like a Group35 with even better specs than either of the above, the Sears DieHard Platinum P-5 Group 35 has a 59 amp-hour capacity. It's has the same AGM benefits, has deep-cycle capability and a great warranty. ...

I find myself in need of a new battery. My local pep boys is recommending a 540 cold crank Boesch battery for 89.90. They have the Optima Red Top in stock fo 154. Is this a good price or can I get an Optima cheaper online?



Thanks

I'm going with an Odyssey 925 MJT. It's "only" 380 CCA, but there are other things to consider. From the specs, it'll deliver plenty of current for 30 seconds and it's never taken more than about 2 seconds for my car to start. If you gotta crank enough to require a monster battery, there's something else wrong with the car. What it does do is take 20-25 lbs right off the nose of the car. Being smaller it also lets me open up some space behind the radiator for better cooling. The stock "box" the battery sits in isn't for better cooling, it's for venting corrosive fumes generated by all wet batteries away from electronics and connectors. The dry cell Odyssey generates no such fumes, plus can't spill acid. Summit Racing sells them for about $175. If you have a mega-sound system, it's might be too small. The red-top in my other car barely made it through this winter and is due for replacement at 42 months, BTW.

http://www.odysseybatteries.com/battery/pc925mjt.htm

check prices; you might have a problem finding a decent battery for $60 these days. The interstate battery cold-weather recommendation runs over $135 -- for a "flooded" type battery. Their "standard" class 35 battery is still over $120. Even their el-cheapo offering is over $100.

So, not 3 times as expensive; more like 50 percent. Will a deep-cycle last 50 percent longer? Imo, it could but that doesn't even matter. I'll probably replace mine at 4 years whether it needs it or not. More important to me that it be trouble-free, i never have to deal with corrosion or maintenance, that it has some guts to get me out a flooded situation, and won't weaken appreciably if deep-discharged. A cheap flooded-type battery might sound like a bargain, but how much does it cost to replace cables and terminals due to corrosion? How much for a tow? For a few more bucks per year i like the peace of mind and total lack of hassles.

+ 1

Looks like $160 plus shipping from Summit Racing online for the Red Top and they're typically a good price. So, your Pep Boys is competitive. Autozone was over priced when I checked last summer but might be better now as well.

http://www.summitracing.com/parts/ULT-9020-164/

I find myself in need of a new battery. My local pep boys is recommending a 540 cold crank Boesch battery for 89.90. They have the Optima Red Top in stock fo 154. Is this a good price or can I get an Optima cheaper online?



Thanks

Looks like $160 plus shipping from Summit Racing online for the Red Top and they're typically a good price. So, your Pep Boys is competitive. Autozone was over priced when I checked last summer but might be better now as well.

http://www.summitracing.com/parts/ULT-9020-164/

With something like a battery, it's always advantageous to be able to not have to deal with shipping in the event of making a warranty claim.

^ I was just rendering a comparison, not advocating shipping a battery. Heavy/costly and as cited a chore to get warranty replacement.

Hi I have been reading all the threads and all signs lead to buying an optima battery. However the 35r is not instock in the UK. I have tried all the online stores and they all say they havent had it in stock for a while.

http://www.optimabatteries.co.uk/ Could some one have a look on this website and tell me which red top exactly i would need. My current battery has problems starting in cold.

Also could you advise me on how dificult it is to fit these batteries.... Are any modifications needed... or do they just slot in. I have an 2004 Model.

Thanks

The Optima Red Top comes with a plastic standoff since it isn't as tall as OEM, but otherwise straightforward.

9020-164 Optima RedTop

http://www.summitracing.com/parts/ULT-9020-164/

What's the difference between the 9020-164 and the 8020-164 that the Optima website suggests?

Hi I have been reading all the threads and all signs lead to buying an optima battery. However the 35r is not instock in the UK. I have tried all the online stores and they all say they havent had it in stock for a while.

http://www.optimabatteries.co.uk/ Could some one have a look on this website and tell me which red top exactly i would need. My current battery has problems starting in cold.

Also could you advise me on how dificult it is to fit these batteries.... Are any modifications needed... or do they just slot in. I have an 2004 Model.

Thanks

The "OPTIMA® YellowTop R 3,7 " looks to be the proper group35 size, which has the terminals in the correct locations. It should come with a plastic "spacer", which goes under the battery to raise it to the standard height. This is needed for the RX8 due to the positive terminal attachment.

Their "red top 3,7" looks to be the proper size but terminals are reversed. With a bit of work you can fit that battery; you just need to rework the attachment cable -- see the DIY section; there is a whole thread on fitting Optima batteries.

http://www.rx8club.com/showthread.php?t=33340

My yellow-top install is on page 3.

If I were you I'd go with the yellow-top, it's the right size and terminals in the right locations. As long as they include the spacer, it's a direct drop-in replacement. It makes a good starting battery.

If your heart is set on the red top, then reworking the cables for the 3,7 isn't too hard. Alternatively, the red-top 4,2 with reversed terminals might fit without modification, though it's 1/2 inch longer. There is a white mark in the battery box which serves as a fitment guide. The end of the battery should not extend past the white mark. This is to provide adequate cooling. Check the measurement.

I figured out the part number difference is the box the battery comes in.

But now this whole reversed terminal thing, some people day it fits perfect, then others say the terminals are reversed. Then when you look up 35R it doesn't exist, so why would Optima suggest a battery for the RX-8 that wouldn't actually fit?

The "OPTIMA® YellowTop R 3,7 " looks to be the proper group35 size, which has the terminals in the correct locations. It should come with a plastic "spacer", which goes under the battery to raise it to the standard height. This is needed for the RX8 due to the positive terminal attachment.

Their "red top 3,7" looks to be the proper size but terminals are reversed. With a bit of work you can fit that battery; you just need to rework the attachment cable -- see the DIY section; there is a whole thread on fitting Optima batteries.

http://www.rx8club.com/showthread.php?t=33340

My yellow-top install is on page 3.

If I were you I'd go with the yellow-top, it's the right size and terminals in the right locations. As long as they include the spacer, it's a direct drop-in replacement. It makes a good starting battery.

If your heart is set on the red top, then reworking the cables for the 3,7 isn't too hard. Alternatively, the red-top 4,2 with reversed terminals might fit without modification, though it's 1/2 inch longer. There is a white mark in the battery box which serves as a fitment guide. The end of the battery should not extend past the white mark. This is to provide adequate cooling. Check the measurement.

In the DIY he's using a 75/35 where the terminals are reversed but on pics of the 35, the terminals are the proper way.

im confused

YellowTop D35

Redtop 35 8020-164

Get one of the above, it will fit 100% nothing special needed.

I got a Sears Platinum (it's a rebranded Odyssey drycell):

http://www.sears.com/shc/s/p_10153_12605_02850035000P?vName=Automotive&cName=Batteries+%26+Chargers&sName=Automotive+Batteries

YellowTop D35

Redtop 35 8020-164

Get one of the above, it will fit 100% nothing special needed.

I was responding to the poster in the UK, and the website he's trying to order from, and its available models.

Personally, I prefer the Odyssey batteries at this point, especially when you can get the product from a local Sears and well-warranted. My Optima yellow-top lasted 4 years, could probably have made 5. Ok, but hoping for better.

Hey guys, I'm resurrecting this older thread because of issues with my Red Top battery that I wanted to bring to light. I purchased it in January 2009 (8020-164 35) and since the beginning of the summer it has been dying on almost a daily basis.

When charged up, the engine starts up quickly. If I let the car sit for more than about 12 hours (less if I haven't driven the car a lot), the battery will be dead, or too drained to start. If I leave the stock radio on for 10 minutes, I won't be able to start the car. This is a 19 month-old battery in a car with no stereo or other electronic mods.

I bought the battery from Amazon, because it was the cheapest place I could find at the time. I did read some reviews about shipping problems (broken batteries because of inadequate packaging), but decided to take my chances. What I didn't see initially though were the multiple bad reviews stating that their red tops were dying in under 20 months. Optima has a 3 year warranty on them, but you cannot get warranty service through Amazon, and Optima won't honor it. Okay, lesson learned - get the battery from the manufacturer next time.

But the question is, why are many of these batteries going bad after such a short time? Even as far back as last winter, when my car sat for only a couple days at time, the battery would be dead. I read that Optima was taken over by another company and quality has suffered. Could this be the problem? I was going to try a yellow top, but then decided against it because I really have no need for a deep cycle battery. I may just go with an Interstate, since I've had good experiences with them in the past. Any similar problems with red tops here?

Hey guys, I'm resurrecting this older thread because of issues with my Red Top battery that I wanted to bring to light. I purchased it in January 2009 (8020-164 35) and since the beginning of the summer it has been dying on almost a daily basis.

When charged up, the engine starts up quickly. If I let the car sit for more than about 12 hours (less if I haven't driven the car a lot), the battery will be dead, or too drained to start. If I leave the stock radio on for 10 minutes, I won't be able to start the car. This is a 19 month-old battery in a car with no stereo or other electronic mods.

I bought the battery from Amazon, because it was the cheapest place I could find at the time. I did read some reviews about shipping problems (broken batteries because of inadequate packaging), but decided to take my chances. What I didn't see initially though were the multiple bad reviews stating that their red tops were dying in under 20 months. Optima has a 3 year warranty on them, but you cannot get warranty service through Amazon, and Optima won't honor it. Okay, lesson learned - get the battery from the manufacturer next time.

But the question is, why are many of these batteries going bad after such a short time? Even as far back as last winter, when my car sat for only a couple days at time, the battery would be dead. I read that Optima was taken over by another company and quality has suffered. Could this be the problem? I was going to try a yellow top, but then decided against it because I really have no need for a deep cycle battery. I may just go with an Interstate, since I've had good experiences with them in the past. Any similar problems with red tops here?

It could be the battery, or it could be your car. In addition to replacing the battery, you should check that the car is adequately charging the battery and that there is no excessive current draw when parked. If something is drawing too much power when parked, that's bad for any battery.

Optima was bought out by Johnson Controls, iirc.

It could be the battery, or it could be your car. In addition to replacing the battery, you should check that the car is adequately charging the battery and that there is no excessive current draw when parked. If something is drawing too much power when parked, that's bad for any battery.

Optima was bought out by Johnson Controls, iirc.

Thanks for the info. I'm just not sure what could possibly be drawing excessive current in the stock set-up. The battery life has worsened dramatically over the past month - and nothing has changed with the car. Any ideas?

+1 for optima or napa gel cell sealed batteries. My 1958 has had one in it for over 5 years, I dont leave the car on a battery tender and it starts right up after months of not being driven.

I purchased it in January 2009 (8020-164 35) and since the beginning of the summer it has been dying on almost a daily basis.

I bought the battery from Amazon, because it was the cheapest place I could find at the time. I did read some reviews about shipping problems (broken batteries because of inadequate packaging), but decided to take my chances. What I didn't see initially though were the multiple bad reviews stating that their red tops were dying in under 20 months. Optima has a 3 year warranty on them, but you cannot get warranty service through Amazon, and Optima won't honor it. Okay, lesson learned - get the battery from the manufacturer next time.

I had the same problems with the red top I purchased online. It only lasted about a year and trying to get it replaced under warranty proved to be impossible. I switched to the Sears Platinum Diehard and my problems were solved.

I had the same problems with the red top I purchased online. It only lasted about a year and trying to get it replaced under warranty proved to be impossible. I switched to the Sears Platinum Diehard and my problems were solved.

Many problems reported with the newer versions of Optima! Sears Platinum = Odyssey, which is engineered by the guy who did the original Optimas (the ones that were good.)

FYI, I just bought a brand new battery at Costco for $59.99 when my battery died. You don't get service to install it, but if you're reading this thread you probably don't need it anyway.

Identical battery case, handle, etc. as the one I removed with the only difference being that it had a Kirkland sticker instead of a Mazda sticker (which I assume must be the original from 2004). Hard to beat if this bang for the buck if this one lasts another 7 years...

I'm sure u bought a new battery by now but for thoes who are looking get a 124R-65. Mine is a Parts Plus, available at Smyth Automotive in the greater Cincinnati area. It has a 700 CCA capacity, and fits like a glove in the car!

Guys, what would be the advantage of going from the OEM battery to the optima. Anything worth considering on a new '10 8?

cold cranking amps for one. Battery life for another. Gel celled batteries hold a great deal more power, plus they are safer. I have one in my 1958 that I only run about twice a month, i never have to tender it and its been in the car for over 5 years still running strong.

i've had my red top for over three years with multiple de-floodings..
yes im a flooder, anyway have not had a problem with it. but as stated they were sold and new company might be using a cheaper material for new batteries

yes optima was sold, BUT the guy started up another company so you can still get the original product. try orbital i believe.

Deep cycle batteries are hard on an alternator, but can be drained totally, and recharge just fine. Not all Optima batteries are deep cycle. Remember not to use a regular charger on a glass mat battery

I am mulling over the idea of upgrading my battery too. I see that group 35 is a fit, but I too also saw a 34r that looks very tempting given the "more power" in the cca dept.


As of today, I see that Optima has a red top 34r so the posts look right (pos and neg).

I am going to ask my Sears friend about their Platinum series. If they do have a 34r, then I might just try this option with a chance to return if I can not get it to fit.

I see that Sears has a four year free replacement too. Rather than ordering one online and dealing with warranty issues later....I think the Sears one might be a better option plus the ability to get the 34 r series in as a try first.

Any thoughts on this? Has anyone else tried this?

Thx
Rick


Ps just to had I just saw another post about a 34r optima being added with some work to the casing. I guess I will see if Sears carries a 34r and update my results.

Deep cycle batteries are hard on an alternator, but can be drained totally, and recharge just fine. Not all Optima batteries are deep cycle. Remember not to use a regular charger on a glass mat battery

Do not drain a deep cycle battery completely,20% remaining is the min: any more and the life of the battery will diminish. Most deep cycle work from full - 50%.

I've run deep cycle batteries totaly dead in my camper and they recharged just fine. I have never used a deep cycle battery in any car I've ouned, so the 50% rule is probally a good one. My point was to Optima (glass material) users was to know how to charge it, and to deep cycle users to be prepared to replace your alternator soon!

For thoes looking for a replacement, as I stated on pg. 2 look for a 124R series battery. 700CCA is enough unless u live at the north pole. It fits just like the one that came out. It is an odd series number, so the guy behind the counter might say it doesent exist, but I have one, and it works great!

Got an ACDelco in my eight still strong at 5 years.

On a somewhat related note:

Is there anything wrong with having the battery exposed in the engine bay? I recently popped my hood to check something out and noticed that the cover for the battery was loose; it was only being held on by the shape of the battery. Moments later I saw that somehow, the cover had literally cracked in half, so I took it off.

Now, I know there's nothing wrong with running without an engine cover (It may even be better for ventilation!), but I don't see too many people with their battery exposed. Any advice? Does it not matter?

I did see on another post that a member did in fact install a 34r. His was a Optima Red Top. I did see on Odessy's website that a 34r does exists. Now I just need to check if Sears carries it in a 34r also. Otherwise I will just install the 35 and be done.

Rick


I did look at the 124r that is also born with pretty good specs! I can get that in a wet cell, but as I am upgrading to relieve myself of the acid issues and if I do have a choice of going to a 35 with an option to the 34r, welllllll that 34r will get the job done and then some :).

Volts don't generally drop off; it's the capacity that dwindles (amp hours).


Well when AMP hours dwindle, it is due to the electrolyte neutralizing over time, which in-turn increases the internal resistance in the battery and drops the voltage at the electrodes.

So, voltage does drop when battery runs out and can be used as a measure for battery life.

V(at electrodes) = V(Rated) - V(Internal resistance)
V(Internal Resistance) = I * R(Internal resistance)

As I said earlier, R(Internal resistance) goes up with discharge, hence V(Internal resistance) rises in a linear fashion, which in turn reduces the Voltage you get at the electrodes.

Potential difference is the force that pushes current out of the battery, and if it drops at electrodes, it will not push enough current to crack the starter motor.
So, yes voltage measured at electrodes is an accurate representation.

ok but whats I :P

i got mine from pepboys. but its a good thing that i read this thread. next time ima get optima! thanks!

ive got a duralast gold series in mine, been going strong in the completely screwed up texas panhandle climate for 3 years now, would have to look at battery but i think its 700 cca and 51ah and 100 reserve minutes which is pretty good for the smaller battery sizes

As an ol' EE myself I'm not arguing the equations with you, I was prior just pointing out that you can still have ~12 volts but low capacity, and it's the cranking amps that are most important (esp. cold cranking to overcome starter 'locked rotor').

Well when AMP hours dwindle, it is due to the electrolyte neutralizing over time, which in-turn increases the internal resistance in the battery and drops the voltage at the electrodes.

So, voltage does drop when battery runs out and can be used as a measure for battery life.

V(at electrodes) = V(Rated) - V(Internal resistance)
V(Internal Resistance) = I * R(Internal resistance)

As I said earlier, R(Internal resistance) goes up with discharge, hence V(Internal resistance) rises in a linear fashion, which in turn reduces the Voltage you get at the electrodes.

Potential difference is the force that pushes current out of the battery, and if it drops at electrodes, it will not push enough current to crack the starter motor.
So, yes voltage measured at electrodes is an accurate representation.

As an ol' EE myself I'm not arguing the equations with you, I was prior just pointing out that you can still have ~12 volts but low capacity, and it's the cranking amps that are most important (esp. cold cranking to overcome starter 'locked rotor').


Yes Huey, depending on the current I being drawn by the Galvanometer and the car itself, it might be 10-11 Volts for a discharged battery.

It mostly depends on the current drawn. But internal resistance is a killer, cant imagine how this is prevails even in the newer carbon nanotube batteries. I guess resistance is nature's way of telling us that we cant surpass a few limits.

Nice to meet a fellow engi. Cheers!

As an ol' EE myself I'm not arguing the equations with you, I was prior just pointing out that you can still have ~12 volts but low capacity, and it's the cranking amps that are most important (esp. cold cranking to overcome starter 'locked rotor').


Right on Huey!!


Star Date Captain log: Sept 20, 2010.....as of this time Sears has an online sale for the Platinum Battery. You can order online and then pick up at the store.
An AGM Battery and FOUR years free replacement pretty much a $40 premium over a regular battery with an additional year warranty free replacement does it for me!

I'm also looking to buy a Battery Tender Plus unit. Nice charger for the AGM batteries and has a great warranty 10 years!!!

Thoughts?

Rick

^ I keep a Battery Tender (and rodent sonic deterrent) on my hybernating '8 all Winter. A great investment.

If you understand and respect the value of Amperage and Torque, life as you know it will be good!

^ "Torque does the work, but horsepower gets the credit."

-or- Amperage does the work, but voltage gets the credit. ;)

But there won't be any current without potential difference :p

^ When powerwashing the deck I'm availed of high potential difference (water pressure) and low capacity (volume), but when in the shower I like relatively low potential difference and high capacity - just like my '8. ;)

^ "Torque does the work, but horsepower gets the credit."

-or- Amperage does the work, but voltage gets the credit. ;)

Volta was always a Prima Donna. :lol2:

I had the same problems with the red top I purchased online. It only lasted about a year and trying to get it replaced under warranty proved to be impossible. I switched to the Sears Platinum Diehard and my problems were solved.


I'm having the same problem as well. Bought it new from Amazon in Jan of 2009 and my Red Top is dead.

Optima Yellowtop ftw.

I'm going with an Odyssey 925 MJT. It's "only" 380 CCA, but there are other things to consider. From the specs, it'll deliver plenty of current for 30 seconds and it's never taken more than about 2 seconds for my car to start. If you gotta crank enough to require a monster battery, there's something else wrong with the car. What it does do is take 20-25 lbs right off the nose of the car. Being smaller it also lets me open up some space behind the radiator for better cooling. The stock "box" the battery sits in isn't for better cooling, it's for venting corrosive fumes generated by all wet batteries away from electronics and connectors. The dry cell Odyssey generates no such fumes, plus can't spill acid. Summit Racing sells them for about $175. If you have a mega-sound system, it's might be too small. The red-top in my other car barely made it through this winter and is due for replacement at 42 months, BTW.

http://www.odysseybatteries.com/battery/pc925mjt.htm

Bumping this old thread because the more I read about batteries the more confused I get. Is the battery above a drop in replacement? On the Odyssey site it looks like it's listed as a motorcycle battery. The PC1200 looks OK, but I have no idea. I can't tell what sizes they are, the specs don't show it (?).

I was going to go with the Sears Die Hard Platinum P-5 (OEM'd by Odyssey), until I saw that it is 50lbs. I don't need a tiny racing battery, but I don't want to add that mother either. Don't they have a normal 35 series battery?

Bumping this old thread because the more I read about batteries the more confused I get. Is the battery above a drop in replacement? On the Odyssey site it looks like it's listed as a motorcycle battery. The PC1200 looks OK, but I have no idea. I can't tell what sizes they are, the specs don't show it (?).

I was going to go with the Sears Die Hard Platinum P-5 (OEM'd by Odyssey), until I saw that it is 50lbs. I don't need a tiny racing battery, but I don't want to add that mother either. Don't they have a normal 35 series battery?

I used a PC680 in an e36 BMW 318is. They lasted about 2.5 years. Very small and lightweight.

Also, Amazon made good on the Red Top I complained about earlier in this thread.