> They concluded it had to do with me driving mostly short trips and gave me a battery charger to use once a week or so.

Makes sense if one owns a 1950's vehicle with generator, rather than an alternator, but I would hope new BMWs had something a bit better than 1950's technology for their charging system!

My Z4 sometimes sits for six weeks without being driven or charged, and starts-up with no problem using the four-year old OEM battery.

It is ridiculous for a dealer to say a new vehicle needs to have a battery charger applied regularly due to shhort trips.