Add the battery item like in p10k

[Martian-0007]

Is your feature request related to a problem? Please describe

Not related to a problem

Describe the solution you'd like

I would like an option to get an item with the current internal battery percentage.
I believe a simple Number with percent sign will do the job perfectly.

Additional context

I am switching from Oh-My-ZSH to Fish, and I used to have powerleverl10k there. It had the option to show the battery percentage, when it was not full or wasn't on AC power.