Corrosion from batteries that leaked on Wii Balance Board (more explanation in comment) : r/consolerepair
Source Battery NEW Rechargeable Battery Pack For Wii Fit Balance Board on m.alibaba.com
RepairBox Wii Fit Balance Board Battery Cover🍯Nintendo System Replacement Part | eBay
Nintendo Wii Fit Balance Board Rechargeable Battery
Amazon.com: Yunnyp 3800mAh Balance Board Battery,High Capacity Rechargeable Battery for Wii Fit : Video Games
Amazon.com: Yunnyp 3800mAh Balance Board Battery,High Capacity Rechargeable Battery for Wii Fit : Video Games
Amazon.com: Yunnyp 3800mAh Balance Board Battery,High Capacity Rechargeable Battery for Wii Fit : Video Games
Wii Fit Battery Kit for Balance Board - Walmart.com
Amazon.com: RepairBox Battery Cover for Wii Fit Balance Board : Video Games
Accidentally left the batteries in my wii balance board for 9 years and it corroded the converters away, is it possible for me to fix? : r/consolerepair
Nintendo Wii Fit Balance Board-Bottom ^Battery Compartment ONLY^-Just OK-Clean | eBay