Yes, the Wii U has a battery, but it isn’t very powerful.
Just as in most computing devices, the Wii U will use a button-style battery to power the system clock even when the owner unplugs the console. That means you don’t have to reset the hardware’s internal timekeeper every time it loses juice.
These batteries are common across all kinds of devices. What’s uncommon is how easy Nintendo made it to replace the battery. Typically, one of these coin-cell batteries will last for longer than most people will use a device.
For example, The Legend of Zelda for the Nintendo Entertainment System made history when it released with a battery inside its cartridge so players could save their game. A lot of those batteries still work today, more than 25 years later.
But they do die. If it dies on a Wii U, Nintendo included a hatch that users can screw off to quickly access the battery. The full instructions are in the image to the right.
Replacements are not expensive. Amazon has a pair of Energizers for $1.99.
Again, according to the manual, this backup battery is only powering the clock, so it should last a long time without requiring attention.
Veteran gamers may remember that the Sega Saturn had a little trouble with its battery backup since it was drawing power into a memory unit as well as the clock. This drained the cells faster than just powering a clock would.
The Wii U uses Flash memory, which doesn’t require constant power.