BMW Battery Replacement Compatibility

KNS · 03-10-2024, 07:15 AM

The battery in my 2004 BMW 325i E46 is getting up there in years. When the time comes I'd like to replace it with something smaller and lighter. The current battery is a massive thing that weighs about 45 lbs and has about 850 CCA.

On the E46fanatics site some have replaced their batteries with many varieties of smaller and lighter batteries, one mentioned and that I'm considering is a Honda sized battery, the 51R with about 500 CCA. About half the size and weight of mine.

I recall reading somewhere that you should not go down in size/CCA when replacing a battery - true? My car does not require coding or anything like that. It's electronically primitive compared to contemporary cars. It's a bare bones 325i, no big stereo/amp etc. Doesn't require cold starts on sub zero mornings.
I'd also wouldn't mind going down in size with the battery in my 993, also big and heavy.

Thoughts..?

908/930 · 908/930's Garage

I think you will be ok with a smaller battery in the BMW325, as long as you can keep it secure, not sure if the existing hold down clamp will work. A new 500 CCA likely has more reserve power than a 4 year old 850 CCA, you will likely need to change it a little sooner.

The 2004 530I uses the same 850CCA size battery but it has a computer that is running when the car is turned off and needs the reserve. Is your car used every day? How high is the current draw from the alarm system? Not sure if your 993 has any active processing while turned off.

KNS · 03-10-2024, 11:38 AM

The car isn't a daily driver anymore, it's used once or twice a week. It'll sit for a week and start no problem. Doesn't have an alarm system (that I'm aware of).

Scott Douglas · Scott Douglas's Garage

We had one of those 51R's in our CR-V.
I replaced it with a Group 24 which I recently replaced with a Group 35.
I'd suggest looking at the Group 35 before going with a 51R, which is an oversized motorcycle battery IMO.

Deschodt · 08:55 AM

I had an antigravity LI battery I'd bought for my 991. Hated to lose it to carmax (I resold the car at the height of covid for top $ but kept the $$$ antigravity). I put that in the E46 daily, saved 30 lbs easy... not a single problem but it was similar CCA.. The only caution there is E46s are easily the worst car ever made when it comes to resetting smog readiness codes so be sure to supply a continuous power source while doing replacement if possible, if you live in a smog state!

If I never had to do this stupid drive cycle again I'll be happy.

I really love Antigravity and their reserve power accessed by remote... I'd wait for a sale and pounce. Given the cost of modern batteries that die in 2 years sometimes, the $$$ of those lithium ones and the extra feature starts to be palatable. Some folks balk at cost but will pay way for to lose less weight. I could lift the 991 battery with ONE finger. Removing theoriginal from the 991 made my L4 L5 bulge out. Jsut saying sometimes $$ buys you quality.

911 Rod · 911 Rod's Garage

If I remember my BMW's correctly, they will throw codes if the battery does not meet it's expectations and I had to replace it with the same CCA.

KNS · 03-11-2024, 09:51 AM

Deschodt,

They are pricey! Do you remember the model you use in the E46?

Deschodt · 02:56 PM

Quote:

Originally Posted by KNS

Deschodt,

They are pricey! Do you remember the model you use in the E46?

it was sized for the 991.1 and it fit... I will go look later (in a zoom meeting)
Yes they are pricey. That's why I said to wait for a sale... On sale, you can get it for 2 to 2.5x the price of a normal battery. But for that you get 25 lbs weight savings, a reserve charge accessible via remote - partitioned in the battery (no AAA for you), and longer lasting battery. That is an impressive feature set for the $. But maybe more $ than worth it to you, you decide.

I probably would not do it for a run of the mill E46 beater either. I just happened to have that rescued from my sold 991 and an E46 M3 that could use "de-porking" since it's already heavy (cab). I can confirm it works flawlessly on LI-on.

My main point was do not interrupt power if possible, it's no fun to reset monitors for SMOG (if applicable)

KNS · 03-11-2024, 03:17 PM

^^ Thanks for the info.

Deschodt · 03:24 PM

there ya go.. oof I need some damp rid in the trunk... smells like the wet car cover...

A930Rocket · 03-11-2024, 07:39 PM

I installed a 51R in my 2005 E46 track car and have had no problems, with it only driven on weekends, if that much. I’ve unhooked it and re-hooked it, when doing lots of work on the car. No problems with the ECU or similar. Saved about 20 or 25 pounds IIRC. Also, I’m using the factory battery hold down.