[Mazzella.Chris]

Hey all!

I know this has been at least briefly discussed here before, but I don't see that anybody has ever come up with a definitive answer. What exactly is the purpose of the second battery under the hood that some of the X3's are equipped with? I know some people have speculated that it has to do with the advanced safety features, etc. However, my 2018 X3 had the second battery under the hood, and it had NO options. My 2021 I just picked up Monday evening has NO second battery under the hood, but it has comfort access, blind-spot monitoring, lane departure assist, radar cruise control, etc. At the end of the day, it doesn't really matter. I am just confused as to what that second battery could possibly have been for

[freshxdough]

An auxiliary battery in the engine compartment is used to provide assistance for the vehicle electrical system. During the phase in which the combustion engine is not running, for example MSA start stop, the energy is supplied from the auxiliary battery into the vehicle electrical system.

With an auxiliary battery you could potentially have a smaller rear battery. And vice versa with no auxiliary battery the rear battery could be larger to store more energy.