every once in a while, when i try to start my car, all power is gone when i turn the key, but when it gets back to 'accessory', the power is all back on. it works fine again after i tap the terminals on the battery with a wrench. is this a bad battery? or just a bad connection to the battery from the connectors?

 

Bad connection from the terminals.

 

Sounds like it is just a bad connection. Clean your terminals really good with a wire brush or some terminal cleaner. Make sure that the terminal tightens down good. If if wont tighten down, get you another cable end.

 

ok, i'l have to try cleaning them. thanks!