his battery is under the back seat & NO it's not necessary. Put a voltmeter on that battery - if it's been sitting parked for a while I'll bet it's low on charge - you need at least 11.5 volts to turn starter & run. It's common if it sits for a long time to drain battery. Mine is parked for winter but I have a battery tender on it to keep battery up - stuff like your clock, ECU and other things will drain it down if it sits for a month or so. BMW wires them so alot of things are hot even when car is off.