It's probably a Li-polymer cell and not available easily. Take pictures - be fun to see what it looks like inside.

That's the problem with Li-ion technology. It's got great power density and better characteristics/wide temp range compared to other batteries. The problem is that it's lifetime starts from the day it's manufactured. It's basically going to last 3 years until the chemistry declines and is no longer reversible (capacity diminishes). You can find devices that have a battery that lasts longer but what they do is use a larger battery and charge it very gently so that they are still in the promised capacity level after the amount of time in question. Lupine, for example, does this. So does Dinotte on their new tail light.

J.