You can replace the stock battery icon, but its not an easy job, because it involves editing the framework. However thanks to a new app we can display the battery percentage right on top of the battery icon.
Battery Overlay Percent, can display the battery percentage right on top of your battery icon, i.e by overlaying it.
The app will work on any device running Android 2.1 and up, and it DOES NOT require root.
On many devices you do have a “Show battery percentage indicator” in the stock ROM, but it uses some precious space in the status bar.
You can customize the position of the indicator, the text size, the text color,too.
I had to manually set the overlay on my Samsung phone but it worked fine by default on my Nexus 7.
Download Battery Overlay Percent from:
Thanks to Krish for the tip.