Originally Posted by jfoj

120 = 12.0 Volts with the engine off means your battery is low and/or bad. This means your battery is only about 25% charged. Either it is low or likely has a bad cell.

You need to get your battery charged and tested, however, if it over 4 years old, time to likely replace it!

Low batteries in these cars makes them go crazy.

Probably time to buy a battery.

DL49 is what many claim fit most everything except convertibles or M3.