Well we will see in a few hours I guess. My batt sits at 12.8 and 13 when it's fully charged when it's at 12.5 I hit the button for % and it's nowhere near 100% not sure if that means anything. If a battery is bad not only will it have to charge a few minuets the car jumping it needs to be big enough as well. Had a rice burner trying to jump a caddy revving it and all kinds of stuff. I said let me try he argued with me man I have a red top if I can't do it you can't. The caddy owner finally let me try cranked over first try. I looked at him and said I have a 160amp alternator and my battery is twice as big as yours the guy was butt hurt LOL