911 charging problem

[Elfer]

Im hoping that you guys might be able to help me out in this matter. Heres the deal: My battery died on me a few days back so I thought it was just time for a new battery. Went out and bought a new one and that lasted for about 2 days. The old battery charged fine on another car, and the new one that was just recently drained of all its juice also charged ok. So which leads me to believe that its a charging problem. My question is that if the alternator is defective, shouldnt the car be undrivable?
With a fully drained battery, I could jump start the car with cables and would run fine and normal until I turn the car off. After which, the car wouldnt start because the battery is drained. I once had an unfortunate but same experience on the road with a Camry, where the belt had broken off. Couldnt start the car with a jumper. Could this be something other than the alternator? Any suggestions and assistance would be greatly appreciated.
Thanks in advance.

[john walker's workshop]

you need to put a voltmeter on the battery and see if the charging voltage is in the 13.8-14.2 range. if the battery is not charging, the lights, fuel pump, radio, etc, eventually drain it and the car won't run anymore. the starter may be the problem otherwise. also check the ground from batt to body, and ground from the nose of the trans to body, as well as clean, tight battery connections. post the year of your car for best advice.

[Elfer]

John,
The car is a 76 911. The car is definitely not charging. When jumpstarted, the car runs fine, as if nothing is wrong. As soon as the car is turned off, it wont even crank. The starter is definitely not the problem as it cranks and starts with a fresh battery or when jumpstarted. What other parts could be causing this aside from the alternator? Would the voltage regulator cause something like this?

[tobluforu]

I'm not an expert, but yes it could be the voltage regulator. Mines located next to the cdi box. My little idiot light was glowing red so I tapped the reg. and all is fine. Except I probably need a new one. Not sure if yours is an internal or externalone or not. Check you book. Do what walker suggests.Also, Is your idiot light glowing? If not, either your idiot light's bulb needs replacing, your reg. is shot or your alt. is gone. Start w\the easiest.