A CMOS rechargeable battery is like the battery in your toy car or flashlight, but it is used in a special type of computer chip called a CMOS chip. The CMOS chip is important because it helps your computer remember things even when it's turned off, like your password or your favorite website.
This battery is rechargeable, which means you can use it many times! Just like how you can plug in your tablet or phone to charge it up, you can charge up the CMOS rechargeable battery by plugging it into a special charging device.
So, in summary, a CMOS rechargeable battery is a special battery used in computer chips that helps the computer remember things even when it's turned off, and it can be recharged many times by plugging it into a special charging device.