Classic/Antique Car Repair: 1948 Desoto battery constantly draining until it wont hold a charge, current cut, trunk light

Question
1948 Desoto; Still 6 volt. It seems like I'm going through batteries every 3 or 4 months. (Duralast from Autozone with 2 year warranty)All of the batteries are draining to the point whereas when I bring them in to get charged, they are useless. Autozone gives me a new one. No charge. Nevertheless, "Houston. We've got a problem!" I had the generator rebuilt 2 weeks ago. Battery replaced today after only in for 2 1/2 months. Thanks.(In advance.)  

Answer
There are two possibilities. 1. There is a drain like the trunk light is staying on. The easiest way to check to make sure that lights like trunk of glove box are turning off is to open the trunk or glove box and immediately feel the bulb. If the light has been staying on it will be hot. 2. The generator is not charging the battery fully or you are not running enough to keep the battery up. Remember that the generator will not charge the battery at idle. That is one reason that the industry went to alternators. They will charge at idle. The voltage regulator could be adjusted too low or the current cut out in the regulator could be sticking and causing a drain on the battery.
A question, how often and for how long do you run the car?
Let me know, Brad