First if this is allready somewhere else covered then sorry guys but at least I tried to help. I wanted to do this because I went true 3 days of googleing to find no information anywhere about the 34R optima red top with an RX8. Optima recomends 35 series but those fit without any modification but you would need and 35R verision. I went with an 34R just because its the same price but 140 cold cranking amps more. 34R does fit in your battery box because its the same size as the 35 but needs a little modification and 10min of your time. Tools regular wire cutting pliers and a knife that will cut the thin plastic. You can use anything else that would get the same stuff done but thats what I had on hand. To make this Short I have attached pictures.

1. Image 100 is the fitment picture
2. While the Battery is in the box test fit the positive and mark where the plastic is hitting on the battery box.
3. Cut out about 3/4" to 1" deep. Look at Image 101 and 102 for referance.
4. Test fit the positive connector that should fit now all the way on the battery.
5. Tight up the positive and negative put back your battery cover reset your DSC and enjoy your red top 900 cold cranking amps. Image 103 and 104 for referance.

P.s. I had very bed problems with starting and thout it was my starter. I had a new battery in there that was stock so before buying a starter I wanted to try an optima or any stronger battery just for the hell of it. After putting this red top in car starts faster then it ever did. I hope this will help some people same way it halped me and saved me at least $200.

 

Cool. FYI that piece you cut just pulls up and off so it would be easier to cut out of the car. The battery box is actually in two pieces. I did not know this and it was making removing the whole battery box very difficult until one of the guys pointed this out to me

 

I hope you have good results with this, but per Mazda that battery is physically too big. See that white paint on the right-hand edge of the battery box, towards the front of the car? That is a fitment mark, and the battery should not extend past it. This is to allow cool outside air to circulate (there is a vent into the front of the box that brings in air). Whether or not this makes a significant difference in the real world, I don't know. The Optima's shape may help you since it's not a monolithic block but a collection of cylinders.

 

I like the plasitc on the positive terminal so I wanted to leave it on there and cut my battery box because next summer the battery is going into the trunk and a turbo is beeing installed. The battery is not to big per Mazda because Mazda sells a cold climate interstate battery that is some wired model number something like 24C... and that battery is the same size as the redtop 35 series and has 650CCA. I went to AdvanceAutoParts and had infront of me the 35 redtop and the 34R redtop and put them side to side and the 34R is about 2mm longer then the 35series so optima recomands 35 but you can really go with 34R. Thanks guys for your thouths and ideas but everybody is uniqe in its own way. Thanks again

P.s. The car still starts very fast and good and we here in Vermont are at 13F for 3 days now so the battery works very well.

 

I recently updated my OEM battery to a Red Optima Group 35. Car starts better but I know it can do better. Next thing is to buy the upgraded starter for my 04 rx8 (the previous owner never did the relevant recalls(( the dealership told him that the car passes the tests, whatsoever!!!) I did not though cut the battery box. Instead, I lifted the battery placing a plactic box under the battery.

 

I've put both an Optima 35 and an Optima 34 in my battery box.

They were a significant difference in length once inside the battery box.

The 34 entirely obstructed the air duct on the bottom.

While the 35 at least left some of the duct open.

The cylinderical shape of these batteries do not solve the 34 issue, because once the rectangular riser is fitted on the bottom, no cool air would come in anyway.

The 35 series RedTop went weak at 1 year, 1 month and couldn't hold a full charge. I put in my spare 34 YellowTop while considering shipping/warranty return or just buying another RedTop at Pep Boys, allowing local warranty replacement without the hassle of shipping...

I do not recommend buying these online, they do not last and have poor reputation on the internet outside of rx8clubs.

 

I did the same thing. No cutting on the battery box. just out the riser under the battery and tada... The air issue with the battery shouldnt be an issue since the battery has a nifty cover that covers against the battery. My 34R has been on there about 6 months and still....no problems

 

I also used this process today, the R34 seems to fit perfectly with the optima battery tray. No cutting required, and the tray might help with air flow it seems.
The battery comes with a 3 year free replacement warranty anyway, so I'm not to concerned with the airflow/heat.

-Shawn

 

or you could just get any size battery (within reason) and relocate it to the trunk

 

Unfortunately, that's not a good option for me. I plan on adding small subs there. And the rest of the trunk will be needed for hauling junk for work.
But I do like the idea.

-Shawn

 

I got the redtop 34/78 because they came on sale for $100 at Wal-Mart

Downside was the terminals are on the opposite side, and the factory only gives you enough slack to connect the negative side.

So I bought a single gage battery lead from part source ($15) and extended the positive side like so.

 

Is this the battery tray that you use?

http://www.summitracing.com/parts/UL...9991/?rtype=10

I am pretty sure that they are universal. Took me a few minutes to locate one, but this is all I could find aside from custom mounting trays that cost as much as the battery.

 

^Yeap, that's it. Except it came with my battery, didn't pay extra for it.

 

I gotta go to costco this weekend to replace(warranty) my redtop. Seems like I get only two tries to start my car and then the battery dies. Found this out after cleanning my SSV

 

Cool. Thanks. I am going to order my redtop at the local Interstate Battery place here in town. I will be sure to ask about the tray when I am there.

 

I simply cut some pieces of wood and I put them under the battery..it fits perfectly

 

Got the new Optima 34R in today and have already installed it. It came with the "height adapter" tray. The install was painless and it fit perfectly when used the height adapter tray on the bottom of the battery! No mods required.

 

so I guess im getting a 34r battery once i find a great price.

 

Just bringing this thread back for a quick thanks to all of the posters that had to endure brain sweat to find the perfect fitment and offer comments...
The 35 was a perfect fit with the little "foot" that came as a safety cover... no cussing, no knuckle blood, no brain sweat...
Thanks again!,
Mikey

 

I bought a 34r red last year and never installed, just had a bit if a look and it looks like the positive terminal is too short, ie needs an extender to make it work?

 

Yes, you will need an extender for the 34R.

 

I finally put this in,
and it didn't need a terminal extension,
made a great starting difference too.

 

Outstanding!

 

Can’t believe anyone still buys these, not the same battery it was 10 or 15 years ago.

 

Very true, but last year, they upgraded the warranty on the last one I purchased and it is holding up better than the bunch that I had to keep replacing under warranty.
I have had better results on different vehicles as well. I never had to replace the one I had in the Corvette. Think it was a Mazda issue?