Schwinn Stelth 1000

Ok So first of all Im Not experienced in electric motors or gas powered. I got My schwinn stealth 1000 about 2 years ago. It Was fun for half a year till the battery started crapping out. It only lasts for 15 or 20 mins(If I go slow). It used to last Half an hour at full speed. I want it to Run 2 hours at full speed. So I can Travel About 40 Miles distance. I was wondering if there was a way to replace the Battery with a tractor battery or something bigger ant put a limiter or capacitor or something to keep the Moter from being Fried.