I have a 93 Pontiac Grand Am GT and was wondering if it is ok to charge the battery with it left in the car hooked up or should I disconnect one of the cables first or just take it out of car altogether. I don't want to possibly short something out. Thanks !
Absolutely. In fact it's better if you do charge it that way, so the computer doesn't reset, and you don't lose your radio stations and stuff.
I don't want to possibly short something out
Just be careful to hook up + to + , and - to - , and you'll be just fine.
Read the charger manual thoroughly. Usually, you must hook up the battery first, THEN plug the charger into the power outlet.
What @mmj said, but I would add that if you have a modern vehicle with computers it is probably best to only do this with a modern type battery charger that provides clean power.
If you have an old-school brute-force charger that consists of little more circuitry than a transformer and selenium rectifier the output is pretty dirty (not filtered at all, it's choppy DC) and you probably would not want that feeding into a modern car's computer modules. (I have a couple of chargers like that from the 1970s.)
modern power supplies aren't terribly "clean" either. Especially if you buy a cheap one.
Instead of nice smooth rectified transformer 120Hz ripple, you get very peaky kHz switching noise , often in the audible range.
