How long to charge car battery?

There's no set value, it depends entirely on the battery and the charger. Can be anything from minutes to the better part of a day.
The time to recharge batteries depends a) on what device you are referring to - laptop/ mobile phone/ MP3 player/ electric car... and b) most importantly, how low the battery already is. Generally speaking, a few hours should suffice for the majority of batteries. Leaving them to charge overnight though may be a wise choice, to be safe.