This is what happened to mine. Do you reckon it was something to do with the bodywork then?
Nothing to do with the bodywork. If they left it standing for a while without the battery on charge and it goes flat they never seem to recover. Happened on every BMW I've had, once it's gone flat a couple of times and then left standing around for more than a day or so it struggles to start or won't start then it's time for a new one.
Gave me an excuse to go and get a nice new one though, the old one last well but over the past 12 months has started to fail in a few areas.