Pay close attention to certain information about their devices such as memory usage, battery temperature, battery percentage and so on.
My BB Bat is a small app (40.3k) by nisido that monitors your battery and tells you at a glance some quick information about its status. After installation, device reboot, or battery charging, the app calculates the residual level of your battery, or how much time you have left before your battery is empty. As your battery level decreases, the app recalculates the residual level to the nearest 10%, and reflects that amount with an indicator on your home screen. So for example, if the app shows that you have 1 hour and 45 minutes of battery life left, the indicator would show a 2 on your home screen. Personally, I like that it shows actual time left as opposed to a percentage because I don't have to try and calculate how long that percent might last me.
The app requires no set up or interaction from the user. You install it, wait a few minutes for it to gather information and calculate your stats, and that's it! Other information that My BB Bat shows includes battery status, level (as a percentage), temperature, voltage, and uptime. Best of all, it's free!
Download my bb bat