I use Battery Monitor Widget by 3c on my tablet, which I mainly use around the house or on overseas trips. It's a quick glance at battery status and also monitors the secondary battery in my Asus Transformer's dockable keyboard.
When out-and-about with my phone, a Nexus 5, I prefer
Battery Monitor Widget Pro from fsinib. It provides several widgets and I use the one arrowed in the screenshot below as it has a little more information I like to see. I've presented it on this screen for scale but normally it resides on my messy Home screen. Excuse the Glitter wallpaper background; it's set to change colours randomly and this is not one of the better ones!
