There is a problem with your charging system. May be a defective alternator or something else.
your battery is dying or is dead
trunk
you dont
In the trunk
12v
In the Boot! right hand side...
reset service engine light on BMW 325
Nothing to reset except radio presets and clock.
Your battery is in the trunk most likely, on the passengers side underneath your small tool carrier.
try looking in the trunk for the battery that's where BMW puts then sometimes. look behind the side panels or under trunk floor
The original BMW style battery is the best option for you vehicle, I believe it is a 720 CCA rated battery, if not Douglas is the company that was making batteries for BMW at that time so you can try to locate a Douglas dealer.
in the trunk right hand side under a plastic protector