If you're simply wanting to be able to go further, then maybe you should consider adding a second set of 2 12V batteries to make a second 24V battery source and a center-off toggle switch so you can switch between the two sets of batteries. The Currie Kit I installed this summer allows me to add a second 24V battery. The power toggle switch, which is a center-off toggle, can be switched to run off the appropriate battery pack. If you have a rear rack you might consider creating pannier bags to hold 2 sets of 12V batteries. Here's a You Tube video that shows such a mod on an ezip--this ezip owner has 2 sets of 24V 20AH SLAs.
http://www.youtube.com/watch?v=qHYfW...eature=related That would give you a lower center of gravity and might make it easier to ride the bike. Good luck.