96 Century kills batteries, why?

[GM Owner]

If the car sits more than a day it won't start. I put in a new battery and that was great for a few weeks until it wore down the battery. I've checked the fuses, lights and nothing looks out of the ordinary. Last year I replaced the computer, alternator, waterpump, belts and had it tuned up...it has 107,000 and runs not bad, just no leg room for the driver. Any suggestions as batteries are expensive to keep replacing.

[bignoisey]

Is your alternator really charging your battery? Sometines one diode can go out and reduce the charge capacity to nearly nothing.
Also, either some light or accessory may be on that should be off, or some other component is draining current (like your alternator) when it shouldn't be. What I'd do is to be sure any lights like the dome light, glove box light, under hood or trunk lights are really turning off when they should be. These may use mercury switches that can turn the light on when the hood/trunk open to the proper angle. If you park on any kind of slope the switch could turn on a light while parked if only slightly misadjusted.
You might have the alternator checked for current leakage when its supposed to be off. Its not easy to tell you how to do this yourself without a wiring diagram, but one way to tell by yourself is to disconnect it overnight to see if the battery stays charged. If it does then you have the answer. Other electrical components could also be tested in this manner by disconnecting them or removing appropriate fuses.

[GM Owner]

Thanks for the info. I will try that. I just installed a brand new battery and so far so good. I put the intereste battery that was in the car on the charger just waiting for the car to kill the new battery.