Have you tried resetting the power manager?
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articleMany places I've visited say that discharging Li-on batteries regularly is really not a good idea. You may indeed have changed the ability of the battery to hold a charge by exposing it to such high heat.
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Li-ion batteries are quite different from previous designs such as nickel-metal-hydride and nickel-cadmium. Li-ions do not require and should not be subjected to regular deep discharges. Maybe the initial discharge Apple apparently suggests for new batteries is useful, but it's not something you should do regularly.
Buchmann also reports that, while it has many benefits, the Li-ion design also has an essentially fixed life, which means you need to budget for replacement in three years or so regardless of how you use the batteries, or even if you don't use them at all.
Here's another idea to try:
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resuscitating Mac laptop batteries in Mac OS X:
[Rob Wyatt] I'd like to share a recent experience with my iBook (white, dual USB, 600mHz). I hadn't used it in a few weeks and when I turned it on, the battery was completely dead. I booted up the machine and was very surprised to find that the battery wasn't even recognized. There was a little "X" over the battery icon in the menubar (OS X 10.2). I attempted to re-seat the battery, zap PRAM (using the key combo upon startup), and reset the Power Manager. Nothing worked. So I called tech support and they had me do all of those things over again. Finally they agreed to send me a new battery.
In the meantime, I decided to try one other thing (after reading about iBook battery issues somewhere online). I booted into Open Firmware and typed "reset-nvram", followed by "reset-all". Surprise, surprise...my battery came back to life and recharged fine.
But do try the power manager reset first.