Where to buy battery

Would you be able to post an image of the old battery? Often times custom battery packs are obscure and cannot be easily obtained, but depending on the cells I may be able to see if I can find you a source to purchase new battery cells to repair/rebuild the old battery yourself.

It seems like a 3cell lipo, about 2000mAh you should get something suitable in rc.model shop....

Original battery - it is actually 2 x 1000mAh batteries so I replaced with a single 2000 mAh battery. The limiting factor is the compartment size which is about 54mm x 34mm by about 10mm thick. Note this has a third wire for thermal protection. Btw the number 553450 refers to the size (I guess 55mm x 34mm x 5 mm but since there are 2 batteries the last 5 is actually 10mm)

Replacement: the replacement number refers to 10mm x 34mm x 50mm so a bit shorter which is fine.

Wires were too short and connection was too small so had to solder on old wires with connection: (CAUTION: Lithium Ion batteries are extremely flammable and dangerous so use caution or find a better replacement)