Comment 17 for bug 1693155

"New icons" might not be strictly required.

If someone can edit: /usr/share/icons/ubuntu-mono-dark/status/{22,24}/battery*.svg
and change them to actual squares of the correct dimensions (22x22, 24x24) then I think that would be a proper fix. It does require editing (recentering) the curves though, and not just changing the canvas dimensions. So you would need a proper vector graphics editor.