I am an Android Application Developer and recently a free android app is developed by Fat Brain "Last Message".
This app is a customize and smart solution to the low battery problem. Users can set the app to notify someone through Twitter, Email, SMS or Facebook to warn them that you may not be in-contact once your phone battery has been depleted. It runs in the background of the device and monitors the battery.
Users can personalize the away message in anyway they’d like and even choose at what percentage they like the app to send the message. It requires Android 2.2 or higher.