my 01 civic cutting off and does not start without jump start and it runs fine until power supplied from another car when I take jumper cables out it runs for a minute or two and stall. battery shows 12.75 volts on meter. but cat does not start till I have jump start it. I replaced the alternator but still doing the same please help

 

First make sure the battery terminals are connected well. When you turn the lights on there should be no voltage difference between the battery post and the terminal. Put one meter lead on each, should measure less than .01 volts. Repeat on both the plus and minus sides.

Start engine and measure voltage at the battery. If less than 13.5 volts, the charging system is not working. Make sure alternator is turning. Measure voltage at the output wire on the alternator it should be the same as that at the battery. Check alternator fuse. Don't assume that a new alternator is good.

Measure voltage at the battery posts while someone turns the key to try to start (jumper cables not connected). It is important to have the meter probes on the lead posts that are part of the battery, not on the terminals that are part of the car. If this voltage drops below 9 volts, the battery is run down and / or defective.