Battery Indicator by Darshan Computing
is my preferred. Sits in the notification area, displays a percentage, and System Panel and Spare Parts both show it using 0% resources. It displays battery health, temp, and exact voltage of current charge. Even has a built-in "disable lockscreen" option. For $.099 you can get a higher resolution image and customizable 4-color (red/yellow/gray/green) indicators.
(I'm not the dev, I just really love this app. If I could replace the built-in indicator with this thing, I'd do it in a heartbeat.)
QR Code for those interested.