One of the things I hate about my Pebble is the lack of a battery indicator. At this point I know more or less how much use I can get off a charge, but there are still times when I'll forget to plug in and my battery will flat-out die. The only notification you get is that tiny little low battery on the menu screen — not the greatest solution. With the updated firmware though, this is less of an issue since there is a low battery alert built in as well.
I did come across a very cool app though that lets you check your battery status whenever you want. It goes by the name of Battery Lifetime and not only shows the remaining battery percentage, but also estimated days remaining as well.
The watch face shows a giant battery and percentage indicator which should be easy enough for anyone to read, but also has a set of 7 dots along the top which tell you how many days (roughly) you have left on your battery — very cool.
iPhone users can search under Apps in the Pebble appstore for Battery Lifetime to grab it free. Android users will need to wait a bit or grab the appstore beta here.