or try a hobby shop for a 9.6v rc car battery. that should run you 15-30 bucks.
may be hard to rig that up if his set up is alrady using the li-ion batteries. he'd need new conncectors etc.
I'm sure Ft Lauderdale has a Wally World: These are using the Zip for Ft Lauderdale City Hall
2300 West Atlantic Blvd
Pompano Beach, FL 33069
(954) 971-7170
7300 West Mcnab Road
North Lauderdale, FL 33068
(954) 726-3388
3306 North University Drive
Sunrise, FL 33351
(954) 749-3111
5555 West Atlantic Blvd
Margate, FL 33063
(954) 975-8682
Also try Circuit City / Staples / Office Depot etc.