Do you have the physical dimensions of the old cell? The physical fit should be the only issue. I assume those Powerizer cells have protection circuits on them -- they look like it and they wouldn't be able to sell them retail without them. I'm sorry, I don't have the dimensions of the standard battery. You could take it apart and measure it, and then find a replacement that was the same size or smaller. Also note the lead arrangement.
Any capacity should be chargeable, depending on the end-of-charge algorithm. The better battery-charger chips monitor terminal current so they will accurately charge any capacity cell. The not-as-good chips charge for a certain amount of time (usually 3 hours) and then cut off regardless of the current.
If you do increase the capacity and the charge time does not increase somewhat proportionally, just pull it off the charger and then plug it back in for a second session to "top it off" (in case the charger is one of those time-delay charger may not leave enough time for a full charge the first time).
Do not try to install a cell that doesn't fit, and be careful not to puncture the capsule while you're attaching and installing it. Use minimal heat with a low-wattage soldering iron. If you damage the Lithium Ion battery, overheating and fire could result later on with charging or discharging. Do not install a cell if it has damage to the capsule.
Modern LiPoly construction and composition minimizes the risks, but do take care when handling these cells. Dispose of the old one properly at a recycling center or a store that receives LiIon cells for recycling.
You proceed at your own risk. I offer advice without any guarantee or warranty.
I've worked quite a bit with these cells and charging chips so let me know if you have any questions.
- The Inspector