I released the first version of "Advanced Battery Monitor" towards the end of last year, to not much fanfare at all. I used it and a couple of my friends used it, and that's about it.
But since getting my hands on an Android Wear watch (Moto 360, to be precise), I added a new feature to my graph to also monitor the battery on the watch.
Here you can see my phone + watch battery level thoughout the day today:
The green line represents my phone's battery, the blue my watch's. I use both devices fairly heavily throughout the day, so I'll let you make of these graphs as you will.
The other feature I've added is the ability to export your battery data. The app only keeps battery data for up to a week, but you can export the whole data by tapping the widget to get into the "settings" and using the Export option.
The source code for the widget is available on github: https://github.com/codeka/advbatterygraph
And of course, the widget itself can be downloaded from the Play Store: