Your Android device’s battery life could be a lot better. Sometimes it makes you through the day, but other times you’ll find yourself out late and notice you only have 10 minutes of juice left. You sometimes wonder where all the battery life goes, seemingly leaking away even when you’re not using your phone. If this sounds like you, then JuiceDefender could be the app you’re looking for.
JuiceDenfender lets you take control of your battery life with ease. Before, the only way to get battery hungry apps and services under control was to wade through a maze of settings menus and individual controls for each app, some of which didn’t have any options at all. JuiceDefender simplifies the process of turning off your various radios when they aren’t being used and making sure that  all of your apps’ data syncing occurs at the same time. It also includes emergency mode controls allowing you to save that last bit of juice for when you need it the most.
JuiceDefender is free on the Android Market, but has a companion app, UltimateJuice, that unlocks more features for $5. If you’re just interested in trying JuiceDefender out and testing how much battery life it can save, feel free to just chose the “default” Profile, which will showcase the best features of the app. It will turn off all radios when they aren’t being used (screen off), and only enable them every 30 minutes to perform a data sync. This means that any new notifications you’d be receiving (GMail, Twitter, Facebook, IM clients, etc…) within that 30 minutes will appear at once when JuiceDefender syncs. They’ll also arrive if you turn your screen on, since JuiceDefender figures you’ll be using data then anyway. While non-instant notifications might be a deal-breaker for some, I find the increased battery life worth it.
You can also use the “aggressive” profile if your phone is dying. This profile just takes the default settings and turns them up a notch, only checking for new notifications every hour. You can even set the “aggressive” profile to switch to the “extreme” profile when your battery is really close to death, which will disable all antennas for good unless you launch a “whitelisted” app. Make sure to note the apps you’ll need the most and add them to the whitelist, as no other apps will work. You should only use this profile in dire battery situations.
There are a few customizations you can make by default, and even more with UltimateJuice. Think the 30-minute notification window is too much? Try a 15 minute one. Just select the “customize” profile and you can tweak as much as you’d like. Keep in mind that if an option has dotted lines around it, it’s only available in UltimateJuice. You can get specific about how it treats individual antennas, set up a schedule to, for example, keep your antennas off all night, and even underclock your phone when the screen is off (root users only).

Want to know how much juice is being defended? Tap the “About” tab at the top of the screen and you’ll get a handy estimate. I’ve seen a 1.5x improvement in my battery life over the last 48 hours! That’s a good half a day! JuiceDefender really works, and you’ll notice the difference immediately.