None
i couldn't find battery sense in the market... might be its not available in the region i m in
The few that I've tried, I found non of them did better than WP8's own tiny battery icon that one can tap and see, besides they all eat my phone battery (some like crazy, some less so...). Also non of them updates real-time anyway (limitation...) so I see no much sense to waste space on my home screen... my own opinion though...
I use Battery Tile.
Battery Tile | Windows Phone Apps+Games Store (United States)
I had Battery level for WP8, but Battery Tile is better looking (in my view) and the live tile works better.