The Supersport original BANNER battery failed fairly quickly after I got the car - despite regular trickle charging. It was replaced by the local BMW dealer with a "BMW" battery (no idea who the OEM manufacturer are for BMW).
I've had no problems since.
The M3 now uses a tiny little LI-ION battery - weighing about the same as a tube of Polos. It is trickle charged and always fires up first time.
