AC plug with backup battery.

[Moo Moo]

I want something that uses an AC plug. And switchs when is it unplugged and starts to use batteries. Where is this type of thing?

[itisme911]

4 minutes ago, Moo Moo said:

Where is this type of thing?

This is whats known as a UPS an uninterupted power supply Here is an LTT video that explains it very well and fast.

 

[Christophe Corazza]

I think you are referring to an uninterruptible power supply. It contains a battery that "kicks in" when the device senses a loss of power from the primary source. If you are using the computer when the UPS notifies you of the power loss, you have time to save any data you are working on and exit gracefully before the secondary power source (the battery) runs out.