A battery eliminator is a device that lets you use electronic devices without needing to use batteries. Battery eliminators give electricity to your electronic device from a power source plugged into a wall socket. This way, you don’t have to keep changing batteries all the time, and you can use your electronic device for a long time without worrying about the battery running out.
To explain it like you’re five, let’s say you have a toy car that runs on batteries. Whenever the batteries run out, you need to replace them to make the car run again. But what if you had a magical cable that you could plug your car into, which would give it the power it needs to run, without needing batteries. That’s what a battery eliminator does - it lets you use your electronic toy without batteries by plugging it into an electrical outlet, just like a magical cable.