88911coupe,
Your battery may still read 12 volts even discharged. A hydrometer is a better DIY tool for testing. To charge the battery, remove the ground (-) cable and connect a trickle charger (observe polarity; + and -) for at least 1 day, then check again with the hydrometer. This should tell you if the battery is still okay.
An on-car load test goes something like this with your fully trickle-charged battery:
1. Remove the coil wire from the dist. cap and ground it so car doesn't start.
2. Connect multimeter to the battery
3. Crank engine for around 5-8 seconds while observing battery voltage.
If voltage stays above 9 volts during the 5-8 second period, the battery is okay. If not, it's not ... okay.
Don't let the battery cycle too often (discharge-to-charge = 1 cycle). This shortens the life of a battery.
Hope this helps,
Sherwood Lee
http://members.rennlist.org/911pcars