They Die In Threes part 3

In part 1 the Impala was repaired with a new starter. In part 2 the Mazda got new spark plugs and an ignition coil. Part 3 is the Buick that usually needs a jumpstart of the battery. The reason I had to let the car sit for a length of time before testing for battery draw is that there are several module/computers on a car that don't shut down immediately just because you have turned the key off. They do timeout or go to sleep mode after enough time has passed if the car isn't disturbed. I had opened the hood prior to waiting so that I wouldn't have to open a door to pop the hood later and start the cycle over again. If a circuit is disturbed it will wake a system so I use an amp clamp that goes around the battery cable and doesn't require a connector to be removed. The battery ground cable on this car had two leads so the clamp had to be placed on each, one at a time. The rule of thumb is that I want to see less than 50mA of parasitic draw on the battery with a sleeping system. 

Both leads show acceptable draw. I started the car again and it cranked normally. I put a voltmeter on the battery with the engine running and noticed slightly high charge. That is a sign of a low battery voltage. 

I shut the car off with the meter still connected to see what the battery voltage was. It was just under 13 volts *but* when I turned the lights on and key on it took about 4 seconds to drop to under 6 volts and kill the battery. The connections were tight. Bad battery. 

Tools to diagnose:

Thanks!

G&G Auto Repair