Take the cable off of the battery to charge it. If it is a good battery and it is discharged, it will take all day to charge it or even all night depending on the charge rate. If the battery is drained down and yet charges back up, in less than say two hours, it is probably bad.
If the battery is good and drains down in one hour you have to be getting one hell of a spark when you put the cable on the battery.
Do not put a volt meter between the battery and the cable. A volt meter is used for checking voltage and is not used to complete the circuit. It will tell you battery voltage if there is any drain of any size and little else. A current meter(amp meter) is placed in the circuit and will complete the circuit.
The light idea is a better idea. I use a single filament backup/park/tail light bulb with two wire leads soldered to it with a alligator clip on one lead. A little tape wrapped around the glass at its widest, keeps me from braking it every 5 minutes. When you are laying on your back under a dash , it is easier to see a light out of the corner of your eye than having to turn your head to read a meter.
If the battery is good and you have the test light between the bat and cable, you just have to lift your head up to see if the light is still on as you pull fuses. If no success with the fuses, try taking the bat connection off the alt. They can charge OK and still have a short that will discharge the bat with the motor off.
Actually, a fully charged battery with a one hour drain time would call for a trouble shooting technique that involved looking for smoke.
