Power bank for Macbook Air mid-2012?

Hi there,

I have a Macbook Air from mid-2012 which I totally rely on but which now only holds a charge for 2ish hrs. I want to know if there are any reliable / trusted power banks out there which would allow me to work with the computer away from home in places with no charging points. I've tried to research online but am a bit confused on the language around magsafe / USB conversions. I am not very technical, I just need to be able to plug something in and for it to charge the battery, and not damage the computer.

I have already looked into replacing the battery itself, but because the computer is so old I can only get a third-party one with just a 3 month warranty. This doesn't really seem worth the money as I am sure I'll be back in the same situation fairly quickly.

Huge thanks to anybody willing to help with this,

Alice