I'm an 89 Toyota Supra Turbo driver, and I'm having starting problems.

I've had them ever since I bought the car (bout 4 years ago). Here's what happens:

During the summer when it's hot outside, it frequently won't start after it's been shut off for a couple mins. For instance, I go somewhere and shut the car off and go inside. I come back out 10 - 30 mins later and all I get are solenoids clicking. Wait for 2 hours from when car was shut off (give or take) and it'll start again.

So I know what yer thinking, replace solenoids (there are two on this car). Did that. Next, replace battery. Did that, twice (see below). Next replace starter cables and such. Did that. Have charging system tested. Did that. Finally, replace starter. Did that.

So after all of this, I just kinda learned to live with it. However, last winter, about this time, the battery started going completely dead overnight. So I thought that battery must be toasted and can't handle the cold weather. I replaced the battery (for the second time since I had the car), and it worked great for the rest of the winter. Until it got hot again and started again with the above problem.

Now this winter, the battery just started dieing overnight again. It's completely dead, no lights on the dash or anything. I kinda thought that maybe there was some kind of current drain that was killing it (even though this wouldn't explain the summertime problem) so I unhooked the battery terminals overnight last night. Still dead this morning.

So here's my new theory: During the summertime, the battery is getting boiled alive in the engine compartment. The battery gets so hot that it can't supply juice to start the car until it cools down. As we all know, this isn't good for batterys and all summer long it's slowly being permanently toasted. Once wintertime comes along, the battery is so weak that it can't stand up to the cold.

There isn't any kind of insulation around the battery at all. During the summer, I can drive to work, come out up to 4 hours later and the engine is still warm. It doesn't ever overheat, there's just lots of stuff packed under the hood. Turbo doesn't help either.

So my question to everyone is: Is this theory of mine probable? If so, what's the best way to fix it? Or do you have any other ideas?