Nintendo no longer has replacement batteries, Is ebay a reliable source for oem ones? I know there's a lot of fake oem batteries out there for other handhelds like the psp :
Turnigy LiPo Hobby RC Batteries with 1s Cells (S) for sale | eBay
HPI RC LiPo Batteries for sale | eBay
Model Power LiPo for 1:8 RC Batteries for sale | eBay
Zeee 7.4V 5200mAh 50C 2S Lipo Battery Hardcase Deans Plug for RC Car Buggy Truck 433565031576 | eBay
Amazon.com: Tecnock 1:16 Scale Fast RC Car for Adults Boys, 4X4 Off Road Remote Control Truck, High Speed 40KM/h Electric Monster Toy Vehicle Crawler with 2 Rechargeable Batteries & LED Light for
2pcs Zeee 6000mAh 80C 7.4V 2S Lipo Battery Hardcase Deans For RC Car Boat Truck 463565037629 | eBay
HRB 7.4V 6000mAh 2S 60C-120C LiPo Battery for RC Car Truck Car Losi TR-Plug | eBay