Uh…your supposed to leave the battery in for a complete test, it has to be tested while under load/reving and what not. But i would say the battery…or a bad connection…i had a bad connection on my battery and sometimes the car would SEEM dead but it really wasn’t…cleaned the posts…put new top-to-side adapters on and no more problems except for my lights having minimal seizures that you really can’t see…which itself is probably a bad ground