Battery GO is a free app that pairs with Pokemon Go. Normally, Pokemon Go uses up a lot of battery life. This is because hatching eggs counts your steps, and catching Pokemon obviously requires you to run the game, but Pokemon Go does not run unless your phone is on and chewing through your battery. This app provides an overlay that dims and locks the screen, without turning it (and Pokemon Go) off.
Improve your battery life
A few preliminary tests showed that Battery GO saved about ten minutes to the hour, compared to a phone running normally at full brightness. That's a lot of battery life. Actual results will vary based on your phone's model, as well as other factors (for example, you might want to switch off other apps besides Battery GO and Pokemon Go). This means you can play Pokemon Go for longer, or keep some extra battery life aside for texting and browsing. When you're ready to catch Pokemon or investigate the area more thoroughly, you have the option of tapping the screen to unlock it, or using a pattern lock. As of this writing, the app only features one lock option and one unlock options, as described here, but according to the developer, more are in the works.
Switch on, switch off
Using the app is a fairly simple matter. It creates an icon in your notification bar. While Pokemon Go is active, tap the icon to dim the screen to its darkest setting and lock the touchscreen. This won't really save any battery life on phones where the touchscreen is already dimmed, but it will still lock the touchscreen, which is useful because it allows Pokemon Go to run uninterrupted while in a pocket or bag. There are only a few small caveats when it comes to using the app. First, pressing the power button while Pokemon GO is locked by the app will turn off the screen and thus pause Pokemon Go. This will not usually cause problems, although it can take some getting used to, but on some phones with more pronounced power buttons it may make it harder to use the app in movement-heavy settings like jogging.
It won't catch you a Dragonite, but...
Obviously, this app does not fix every problem you might have with Pokemon Go. It doesn't save as much battery life as Pokemon Go itself could, if it ran while the screen was off. But in terms of what the app does for your battery life when playing Pokemon Go, it exceeds all expectations. Screen usage is what drains most of your phone's battery, and Battery GO provides an effective cure for Pokemon Go's voracious screen usage.