Cadillac Repair: Battery info..., 1989 cadillac fleetwood, port fuel injection

Question
Hi Tom. I just had a question about my Cadillac.  I have a 1989 Cadillac Fleetwood (4.5 Port Fuel Injection V8) and am constantly having to get jumps or battery replacements because it won't crank.  Could you first tell me what you think may be the problem and secondly refer to me the proper battery "size" or "type" in reference to power that I should be using? And lastly there's a mechanism that cuts on and off under the hood (it's not a fan.....just a noise it makes) and I don't know what it is?  What is that and could that be draining the battery also?
I REALLY appreciate your help...

Answer
See if you can get a picture of this item that keeps cutting ON and OFF and e-mail it to me at: onlineautohelp@msn.com.

You can put the largest amperage battery in the car that will fit in the space. Any place that sells batteries can tell you which is the largest one that will fit.