Hey guys,

I replaced my battery with a new one a few months back after mine kept testing bad (following a year of service) and I am continuing to have issues with the battery holding a charge. The new battery tests good, but following a drive it still registers about 100 CCA lower than the specification. If I let it go more than two days without running it is very weak to start. I had guys at an auto parts store do an alternator test and the only issue they saw was when the AC cut on or when the engine revs returned to idle after neutral throttle the voltage would very briefly drop to around 11.2 and then jump back up to 14.4. They said something about a bad regulator but I am not familiar with what that is. The car has no issues starting warm, holding idle, or any drivability problems, so I don't suspect bad compression to be an issue.

Can anyone point me in the right direction? I don't like to drive it but every several days but I am finding I have to take it out just to keep the battery alive.

 

The voltage regulator is responsible for not overcharging the battery. It's possible it killed your new battery over the time it has been used. Drops to 11V don't seem like a problem by themselves, the car is reducing load on the engine while finding idle.

However it's also possible the battery was faulty from the start. It's happened to me. Losing charge while sitting could be poor battery or you could have a phantom current or a lightbulb stuck on (check the trunk light while it's closed) that's draining it. You can test that easily with a multimeter, there are DIY videos.

 

All good advice Loki, thanks. I think that may have been the case with the old battery that lasted a year, I am going to get it checked out. Also didn't even think about the trunk light! Will look today. I had the battery tested about 2 months after buying new and they still say it's showing as 'good' from the tester readout.

 

The alternator output is controlled by the pcm. So it’s not going to output a constant V all the time like a standard alternator. Usual fail symptoms are no output or way too high output; which has fried the wiring and pcm’s on a few RX8’s before. Make sure the main output cable out of the alternator is tightened down properly (nut under the gray plastic pop-top cover). A few people fried that cable by not having it tight, because the pcm is losing the output signal and ramping up output as it bounces on/off the contact surface.

 

Do you have a pic?

 

https://www.rx8club.com/series-i-tro...melted-236300/

 

Yikes. Thanks for the pic, Team. I checked mine and it looks nothing like that. I also checked the truck and it doesn't look as if any light is getting left on. The car barely start today after sitting for two days, I can tell the battery is getting worse so I may take it by the auto parts store again.

Also, Team- what would you consider too high voltage? Anything over 14.5v? From what auto shops have told me anything between 13.5 and 14.5 is normal, but mine consistently reads 14.4ish.

 

Sounds like a significant parasitic drain that needs to be hunted down.

https://www.wikihow.com/Find-a-Parasitic-Battery-Drain

 

Nothing wrong with mid-14V

 

Nice, sounds like I’ll need to pick up a multimeter then. Looking forward to figuring out what exactly is going on.

 

Sounds like either a drain draw from somewhere or a bad battery.

 

The Auto parts store consistently has a read out of “good” on their battery tester whereas my last battery that was a year old had a “bad” readout.

I am going to pull the battery from the car today and drop it off to get it tested again, if it’s bad I’ll get a warrantied one but if it’s reading good I’ll ask about a multimeter

 

It wasn’t clear if the battery was fully checked out or not is only why I mentioned it. If finding the drain proves too difficult you can always consider installing an auto-disconnect battery saver device.

 

Went to start it after it sitting for 3 days and she was dead. Took the battery up to the store and then get hooked it up to their reader and it still says nothings wrong with the battery. They have it on the charger he said if it take a charge then the problem is elsewhere. Been delaying buying the multimeter as I’ve been slammed with work but I’m picking it up tonight on Amazon.

 

It seems that the Law of Parsimony was proven accurate once again. After a few weeks I finally noticed the battery cables were not snug onto the battery post terminals. After buying some HD connectors and fastening them to the cables I don't seem to be losing charge...

I am glad I went the route of crossing off simple things before doing as some shops suggested and replacing the alternator.

Thanks to all who pitched in your .02. Happy the car is running well again.

 

as we discussed by pm, if they were loose the battery likely wasn’t receiving full charge from the alternator, but you’re cranking off the battery draining it. I can’t see the loose connection itself causing a drain, but maybe.

 

Right. I was told by everyone that wasn't it until finally I went back to the shop last week and the mech said that's most likely doing it.