Rechargeable batteries are found in pretty much every piece of consumer electronics these days and are a wonderful inclusion when you want portable power without the need for old-school disposable batteries. However, they don't last forever—and, in some cases, when they reach the end of their operational life span, they can cause damage to your hardware.
You might recall an issue we reported a while back concerning PSP batteries ballooning in size and cracking the battery compartment of the console. It seems that the Nintendo Wii U's GamePad battery sufferers from similar issues, as noted by SlimJimmy on social media:
"After almost 13 years of use, this battery is also getting fat," he says. "I wanted to play a round of Super Mario 3D World with my daughter yesterday and immediately noticed the bulge on the back... Unfortunately, the GamePad doesn't work without a battery, even when plugged in. I'll be ordering a new battery in the next few days."
Mercifully, like the PSP, the Wii U GamePad's battery is easy enough to replace. However, many modern systems—including the Switch—contain batteries which are sealed into the casing, and changing them is somewhat more difficult.
The Wii U has had other problems, too, such as refusing to turn on due to failed components. Thankfully, this, too, is fixable. However, if your GamePad is beyond repair, there are other options.