Corrosion from batteries that leaked on Wii Balance Board (more explanation in comment) : r/consolerepair
Nintendo Support: How to Install the Foot Extensions
Wii Balance Board Battery Case Replacement - iFixit Repair Guide
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
The battery component on my wii fit board have corroded, is there any way to repair this, or do I need to suck it up and buy a new board? : r/wii