Here are a couple of other alternatives to the sealed lead-acid batteries with better capacity per pound available from http://www.texaselectricbikes.com/contact.htm:
LITHIUM POLYMER BATTERY 36 VOLT-15 AMP HOUR
$749.00
THE WAIT IS OVER!!!
WE HAVE BEEN WAITING SINCE 1985 FOR A BATTERY THAT WAS GOOD ENOUGH FOR THE LIGHT ELECTRIC VEHICLE MARKET. WE TESTED PROTOTYPS 10 YEARS AGO, AND FINALY THEY ARE IN PRODUCTION.
THIS IS THE BATTERY FOR ELECTRIC BIKES, ELECTRIC SCOOTERS AND ANY OTHER LIGHT ELECTRIC VEHICLES THAT DEMAND LOTS OF POWER.
NiMH 30 VHF Series Battery
$899.00
SAFT NiMH 36V,13Ah VH SERIES Ni Metal Hydride Battery