This is my first contribution here...so if it doesn't look professional, sorry, I truly did my best.
If you want the percentage of battery to be displayed on the stock battery icon instead of through a widget or notification icon, this is my little fix.
First you need to backup your old framewok-res.apk through recovery mode.
Enter recovery mode on your phone, use adb shell, then
mv /system/framework/framework-res.apk /system/framework/framework-res.bak
now add my new framework-res.apk (after removing the .zip extension, leaving just .apk)
adb push /path_to_your_framework/framework-res.apk /system/framework/
and done, reboot, enjoy.
(20% increments are due to there being only 5 default battery levels in the stock indicator to edit)