Invertor?

[MCavity]

First off – sorry if this has been discussed before.

I have been thinking about using car batteries for a power source. I have a very limited grasp of electrics, and need a device that would work as some sort of invertor to a normal mains plug. I’m looking at it as a short term power boost against brown / blackouts.
Does anyone have suggestions on what would work best, or any idea on the best device out there.
Please keep any technical comments to ‘explaining it to a 5 year old’ :/