For those of you who need to replace a worn battery on your Classic, I'll explain the process here (originally from my own post)
You will need: 1: Your Gamebuino (Obviously :P)
2: A soldering iron (I used my battery-powered iron for this, but a wall-plug iron works just as well)
3: Some Resin-core solder
4: Some double sided foam tape to hold the new battery (I got this Scotch stuff in the same aisle as the wall fasteners in Walmart)
5: a new 3.7v lithium polymer battery. my new one is 600mAh. anything larger then the 250mAh should do fine.
Replacing the battery:
1: The circut board can overheat while you're soldering, especially if you're like me and have to try a dozen times to get a good solder joint. using something like these pliers to hold the board and absorb a bit of the waste heat is advisable.
2: unclip the screen first, it'll make life easier.
3: to remove the old battery, pull gently on the wires while touching the iorn to the pad. they'll come off once the solder softens. remember the polarity!!!! black is negative (-) and red is positive/hot (+)
4: to put the new battery on, remove any connector it has, and use a proper wire stripper to strip the wires, just enough to cover the pad. Next take the iron, and hold the bare wire of the negative line to the negative pad, and keep it there while you reach for the solder. put the solder up against the iron until it starts to melt, you'll see a bit of smoke. pull the iorn away, and then the solder. it should cool and stay in place. repeat for the positive connection.
Testing your work: 1: Attach the new battery with the double sided tape, ensuring the wires aren't in an odd orientation (I moved the battery a bit after that photo)
2: connect a USB power source and see if it charges.
3: If it does, wait until it indicates a full charge. If you put a larger battery on it, this might take a while! it takes several hours to charge mine.
4: then try running some games, or in my case, the settings software. You should now have a Gamebuino Classic with a new battery