I just opened the framework-res file and modified the buttons (one by one) to make them smaller (it should be a maximum of 16 px wide, I made them 16*38). There is usually a waste of space on the left and right sides.
not elegant, but a solution. If you want I can upload my framework-res for you.
That icon is too wide, much wider than 16 px. It will look very ugly squished down.
I don't really have the skills/time to do much, but I have used these icons . They were small enough to fit in the constraint that Samsung have made.
I have also attached my framework-res.apk
Edit: if you want to manually make your own, you need to open the framework-res file on your PC (use 7zip) and change the battery PNGs one by one. Use a software like GIMP (free) or PhotoShop (definitely not free), not MS Paint because it doesn't support transparency.
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