You may consider just getting another battery. One of the main concerns, would be the size of the battery. The mount for the battery is very precise.

Anything bigger would not fit. If your looking for flying times like 20 minutes or so, then you have to consider overheating the motors.

That will shorten the life of the motors. Even after a 8 to 10 minute flight, you should let the motors cool down for 10 minutes or so. I have several batteries, and have flown 2 batteries in a row and the motors get extemely hot.

Just things to consider,

Dave / AKA Choppersrule