[Redd]

Thanks for reviving this old thread! I think it has helped me solve an issue I had with LiFePo4 batts.

Couple years back I tried using LiFePo4 batt. Registered it as a 72Ah AGM batt. The LiFePo4 batt worked fine for the first 200-300km, then strange things started to happen. For some reason, the alt would not charge the batt. It would let the batt run to 0% (even while I was driving the car), I'd have to jump start the car, then the alternator would charge the batt to 100%. After that full charge, it would let it run flat again. Rinse and repeat. During this time there was no increased battery discharge issues.

Alternator checked out ok. Removing and subsequently replacing the IBS battery cable did not solve the issue. In the end I went back to a normal AGM batt and everything was OK again. I never managed to get to the bottom of the issue, just chalked it up to incompatible battery (it was a China brand) and never used it again. Strangely, that same battery works fine in my Alfa 159 and other non-M3 BMWs.

This thread has reminded me again of the weird charging behaviour of our M3 alts. Maybe what was happening is that - for some reason - the DME keeps thinking the LiFePo4 batt is above 70% charge and does not activate the alt to charge the batt. Maybe cos the LiFePo4 current/voltage is high indicating strong charge or something.

With this new revelation I might try the LiFePo4 batt again but this time without registering the batt to see if it makes a difference.