[Nitrousbird]

My E92 is just starting to show signs of the battery dying...some recent abuse by me + extreme cold is the likely culprit. It has some random auto parts store battery in there now.

I can code myself, know I need to reset for the new battery + change battery size/type if needed - I got that covered.

What is the biggest battery I can get that will fit? It looks like the 3 popular sizes are Group 48, 49 and 94R.

49 is the biggest physically and likely to find in the biggest capacities in this size. Anything bigger physically that will fit? I don't care about weight and will probably just do a standard wet cell battery.

I don't care what the BMW dealer says or what the car came with...I want the biggest capacity battery I can get in there (without breaking the bank). Suggestions?

[Sgop335]

I have my orig battery in there, yesterday it was -1F. Based on others as well seems to me oem battery lasts longer. I once looked at aftermarket batts just to be ready cant seem to find a good one. And w the registration thing and all.

Think i will stick w oem, if you like i can dig part number.

[David1]

You don't want the biggest, that just adds weight and the factory ones are heavy enough as it is. I would want to go lighter with the same cca specs. Physical size of a battery does not alays equal it's performance.

[Nitrousbird]

Originally Posted by David1

You don't want the biggest, that just adds weight and the factory ones are heavy enough as it is. I would want to go lighter with the same cca specs. Physical size of a battery does not alays equal it's performance.

- Daily Driver, not a race car. These cars make poor race cars.
- 15lbs is probably the max difference. Weight is over the rear too, which at least helps justify adding weight due to poor traction.
- The good wet cell Group 49 batteries are doing 900 CCA, 1080 CA and 185 minute reserve. What 94R, Group 48 or smaller are pulling off those specs? If any are close with similar cost/lower weight, I'm all for it. I can score a decent wet cell with those specs for $115.

[David1]

15 pounds to me means a whole lot. No matter where it is.

[Efthreeoh]

So I think it is more important to make sure the OEM and physical size and case design is correct for two reasons: 1) the battery clamp mechanism is specific to the design of the case bottom, and 2) the position of the vent tubing. The biggest wet-cell battery is a 90AH 720 Amp BMW P/N 61218381762. I believe it is a DIN-size H7. The battery clamp has positions for a H6 or H7 case size. Also the vent tubing is on the forward-facing side of the battery (faces the wheel well). When my battery was showing sings of weakening, I replaced it with an OE from BMW (I had a coupon for $200 of free parts) and registered it with my BT scan tool and have not had any issues 4 years later. My experience with OE BMW batteries is they last a long time.

[Nitrousbird]

Originally Posted by David1

15 pounds to me means a whole lot. No matter where it is.

I decided to compare the same batteries in different sizes to see the real weight difference. Autozone has a big selection (and all specs posted), so I compared those for an Apples to Apples comparison:

Duralast Platinum AGM:

Group 48: 45.5 lbs
Group 49: 58 lbs
Group 94R: 52 lbs


Duralast Gold Wet Cell:

Group 48: 40.91 lbs
Group 49: 52.01 lbs
Group 94R: 47.41 lbs

So:
- AGM's weigh more and cost more
- 49 AGM weighs 17.09 lbs more than a 48 Lead Acid. Not really a fair comparison
- 11.1 lb difference between Lead Acid 48 and 49, 12.5 for AGM's.

That 11.1 - 12.5 lbs difference in weight gets you a lot of extra reserve power. Unless you are gutting your car to be a track mobile, you will never notice the difference (and again, these are not ideal track cars by any stretch).

[David1]

I don't need any extra reserve. My cars are stored for the winters. The IBS negates that anyways. My mods are all about reducing weight. If there was a good optima battery for our car I would do that but my oem is still going strong after 6 years. BTW, I am about 15 miles from you.