Heat

I also just checked my battery which was at 100%, and it appears to have been completely drained and it is at 14% now after a few minutes of charging.

Okay, now I have a different explanation of what happened as a result of what you've just posted.

When a MBP is working extremely hard, as it is when it's running an outrageously demanding game like Diablo 3, it needs all the energy its AC adapter can provide to power its CPU, GPU, RAM, hard drive, other computing components, and its cooling fans, which are roaring at top speed to try to keep things from cooking. Under those conditions, the first thing that happens is that battery charging stops. The energy that would otherwise be charging your battery is diverted to meeting the unreasonable demands of the game (plus anything else you happen to be running simultaneously). If even that doesn't satisfy the game's greed for power, the battery is drawn upon to make up the deficit. When that happens, you can be draining the battery even though the AC adapter is connected and delivering every watt it can. And if you keep that up long enough, you'll empty the battery and the machine will abruptly shut down or hibernate for lack of power to do what you're asking of it. That's what happened after several hours of Diablo, and that's why your battery was down almost to zero. There was no thermal shutdown; I was wrong about that.

When the battery drains down to nothing, it has to be recharged partially before the machine can be started again. That's why you couldn't restart it right away or for a while after it shut down. When it finally did restart, it tried to resume running Diablo where you'd left off, and as soon as Diablo started devouring power, it killed off the small charge you'd injected into the battery and put you back at square one again. That's Lion's miserable Resume "feature" tripping you up. Turn that off as soon as possible.

I don't use Lion and can't tell you how to extricate yourself quickly from Resume's cycle of frustration, but if you charge the battery overnight, it should have enough oomph by morning to give you time to quit Diablo before it kills your battery again. Then you may find that you don't need your Genius Bar appointment at all -- everything may be fine again. If that's the case, remember the following:

High-intensity gaming is the most demanding thing your computer can be used for. Game developers never, ever do anything to improve the energy efficiency of their products: energy efficiency is not in their universe. They are only interested in bigger bangs, more spectacular effects, greater graphic complexity, faster motion, smoother animation, and more visual detail. This means games grow exponentially more demanding in every new version and every sensational new release, and heaven help anyone who has a limited power budget -- i.e., anyone using a notebook computer with a limited AC adapter output capacity and/or finite constraints on its ability to dissipate heat. Users of desktop computers are free to game away to their hearts' content, as long as they can pay their electric bills: the wall outlet never cries uncle. But you can't do that, at least not in Diablo: you have to pay attention to your battery-level readout as you play, and quit the game when the battery gets down to 20-30% if you want to be kind to the battery. Running it all the way down on a regular basis will drastically shorten its overall lifespan. If gaming is going to be a big part of your life, and you want to keep up with the latest hot games and do it on a Mac notebook, be prepared to buy a new high-end MBP every year. Midrange machines won't cut it. Serious gaming will always require you to buy ten or twenty times as much computing power as anything else you do is likely to need, and if you aren't prepared to pay for that, it would be best not to start.

I believe you were right the first time, and that this second statement refers more to the 13" MacBook and the MacBook air because (the delay between my last post and this one) I was playing Diablo with the graphics set at the highest because I love watching my barbarian smash stuff, and my battery charged a good amount. I'll do another test tomorrow to see if this remains true. Due to my extreme excitement over getting this new beast of a laptop, the graphics are truly amazing, I probably covered the vents in some way that I was sitting so that my legs wouldnt get burned. After the initial crash, I did unplug the charger so this could explain why the battery died also. What do you think it was now? Because I actually increased the graphics, and not only was the fan nice and peacefully quiet, but my computer did not heat up as quickly, and the battery charged while being played.

I'd like to apologize for any confusing sentence structure because it is 1:42 and I'm getting tired. Thank you for your help, it has truly been helpful and your explanations have been great.