We have our E/Moksha solution for wallpapers changing on my github. It is called slideshow. Unfortunatelly it is not in repository. Anyway if you fail with your solution let me know and I will create slideshow deb package for users.
In this link you will find the useful info for you. For now, switch to MokshaGreen theme where I scaled the battery font. If your indicator is still small on the shelf, just put the battery gadget on the desktop as you can see on the picture.