volkswagen passat battery?

That's a classic sign of an aging battery slowing dying from internal shorts. It can test great after a full charge but let it set a long time (overnight) and it's leaked down again. Driving it during the day it gets recharged frequently (by alternator) and doesn't have time to leak all the way dead while parked only a few hours. So, if it's more than about four years old, I would replace it before you get stranded. This based on the assumption your car's charging system is okay.

sounds about right thanks