Low battery warning

Hi Lads, sorry if this has been asked before but a search did not produce any hits, I left my car in with BMW dealer for 2 days for some small collision damage repair. New bumper and grill. When I got it back the battery warning light came on straight away. I phoned them and they said the would have no reason to dissconnect the battery. The only thing I can think of is the had the radio on for the 2 days it was in the shop and the voltage is down a bit. Anyhow, Is there a reset for this or should I just go for a long drive to charge up the battery again?
Its an F10 520D.
Thanks.

There's no reset for this. A good long drive might bring the battery back up but it would be better to put it on trickle charge overnight.

How old is the car. If it's s 2010 the battery might just be dead

Its 2011, I would agree but its just funny it happened as I drove out of the garage. Ill go for a long spin tomorrow and see what happens.
Thanks for the prompt replies lads.

Update!! Guy from Joe Duffy's rang me back today, he said the battery warning if a software issue, He asked me to drop it in on monday for 2 hours for an update. I will let ye know what happens.

Battery warning update, Just got time to leave the car in to Joe Duffy's today. They rejiggled the software and the warning is gone. They seemed a tad sheepish though when handing the car back he said its clear now but if it comes back it will require full diagnostics. WTF?? It was in there from 8:30am till 5pm. And it still was'nt ready when I went to collect it. Anyhow,, heres hoping:smiling:

Update,,, the warning light has not come back since the software reset.