Dual battery question

[andrew.nelson08]

Hi folks, I purchased a 2008 X5 m a few months back and have had some electronic issues. It seems my x5 has a dual battery set up in the back. There are two optima 6v red tops, at 50ah, one on either side. I assume they’re hooked up in series to attain 12v, but that means I’m only running 50ah - correct?

When I use BimmerLink the car shows having a 90ah battery. Seems like whoever replaced the batteries didn’t re code the system to 50ah.

Would this cause electrical issues/error codes?

And could I simply recode it to 50ah or would this mess things up?

TIA




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[80stech]

What the heck? I thought the dual battery setup is supposed to be 2 12volt batteries! Does this look factory?

The TIS says 1 battery mainly for starting duty and the other for accessories.

[andrew.nelson08]

Here’s the other side, I don’t think it’s factory. The IBS system is on the other battery. It looks professional but I’ve noticed other cutoff wiring splices (presumably from a stereo)so figure someone changed something around.


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[80stech]

Yeah, that's a bit of a kludge and that is a fair bit of corrosion on the distribution connector. I would put it back to original with 1 12v Delco pro AGM. At the very minimum load test the batteries and clean up the connections.

And yes, you only have 50A hrs with both in series for 12 volts.

[andrew.nelson08]

So for a stock set up the IBS connection is on this side as well? Is it obvious where it connects onto this hodgepodge?


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[80stech]

The battery should be along the back not on the sides, it is on my E70 at least.

[andrew.nelson08]

Hmm interesting. Thanks for the input.

Still curious if the vehicle having a 50ah battery but thinking it’s running a 90ah would cause electrical demons…


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[80stech]

No, I don't think having it listed incorrectly will cause any noticeable problems.

[andrew.nelson08]

Strange. Thanks!


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[ard]

If you only have 50Ah, yet the car thinks it is 90Ah, it will not charge properly. It may, in fact, be over-charging at times.


The E70 charging system is too cute by half- I would return it to stock: AGM, 12 V, IBS in the right place.... system coded accurately to the battery installed.


Edit: Ive seen some hackery in my time, but this one is...wow...something!