I have a few extra of these nice APC (the UPS people) brand
batteries for sale.
9.6 volts, 3800 maH capacity. More specs to see at:
Looks like a special type of connector, but haven't gotten
a good look at it yet.
Price would most likely be something like mid twenties dollars
plus shipping (from Massachusetts). Less per unit if you'd
Lots and lots of uses for on or off your balloon. Please post
any questions here, and email to order.