1997 buick park avenue battery or charging issue

1997 Buick Park Avenue
3.8
87,000

Just bought it and after the 102 miles drive back home from the used car lot (it ran great) the next morning the battery was dead. Thinking I left something on I jump it and ran all day then carefully check to see if anything was left on and turned it off and the next day the same problem (btw the battery looks brand new). So my questions are...

1. How to check if something is draining the battery when it is shut off?
2. How check the battery being defective or the recharging system?

Thanks in advance,
You will need some test equipment to determine the condition of the battery itself but here is the procedure to look for a parasitic draw.


You will need a digital ammeter and a jumper wire with clips on the ends to do this.
First rig any door switches so you can have a door open without triggering the interior lights and unplug the hood light. Remove one battery cable and attach the meter in series between the battery cable and battery post. Take the jumper wire and also attach it the same way. Leave the jumper wire on for at least 10 minutes to expire all the automatic timers. Now remove the jumper wire and read the meter. Anything over 50ma is too much draw. The way you locate this is to start removing fuses one at a time until the meter drops to normal level. This will be the circuit with something staying on. Determine what components are part of that circuit and check them individually until the problem is isolated.

Your instruction are quite clear and easy to understand but I'm not mechanically inclined...I will try. Should I fail and end up taking it to a shop...what might I expect to pay for this test?
That just depends how hard it is to find the draw assuming there is one. They usually charge by the hour for electrical diagnostic work.

You can test that the battery is charging by putting a multimeter across the terminals and testing that the voltage is 13.4 volts. If it is 12.8 or lower then it looks like a charging problem.

dlamerton; Appreciate your input, but a fully charged 12V battery should have 13.2V. Charging voltage should be no less than 13.6V and no more than 14.6V. A low, or sulphated battery can cause erroneous alternator output.