How generic a topic is this?

Battery 1 = came with the car. I found the radio code and hooked up the antenna connector (the one for extending/retracting). I also used the remote window up feature everytime I left the car. Within a month the battery died.

Battery 2 = I removed the radio and disconnected the antenna. I noted a 3 amp drain whenever I hooked up the battery. Seemed high so I disconnected the battery whenever the car would be parked for more than 4 hours. I mean I disconnected the battery right after shutting off the engine. After a couple of months, the battery remained disconnected for 3 months while the engine underwent a rod-ectomy. I hooked up the battery and ran it down bleeding the IP. I got the engine running with another battery then reverted to battery 2. Didn't use the remote windows up feature. Battery 2 lasted a couple of weeks, with the same disconnection regimen, then died. Shop test showed a dead cell, if I understood what they were telling me, and got a new replacement with no pro-rated charge.

Battery 3 = Radio and antenna still out of the loop, now disconnected the radio amp. I didn't disconnect the battery when the car was parked. Used the remote windows up feature once or twice. After a month, battery died.

By died I mean the battery doesn't have enough juice to turn the starter. Starts easily with a jump.

The charge light comes on while glowing and goes out quickly and stays out when the engine fires. Does this indicate that the alternator is fine?

Regarding the 3 amp drain, it's possible my DVM is bad or I'm not using it properly. Still looking for an affordable clamp type DVM to make this diagnosis easier/foolproof.

Any thoughts on what I should do next?

Thanks,
Sixto
93 300SD 3.0