Android: Most phones doesn't make it easy to switch mobile data connection on and off, even if doing so really helps save your battery. JuiceDefender toggles telco data and Wi-Fi on and off every so often to preserve power.
The whole point of a smartphone with Google apps baked in is constant connectivity, of course, and you don't want to shut off access to your email and other online services. But when you're walking around, at your office desk, and generally not actively using your phone, you probably don't need your phone to check in every minute with the mothership. JuiceDefender lets you set a time interval — five minutes, 15, 30, an hour, two hours — at which its background process will re-enable your carrier APN, see if there are new messages or data coming in, and then shut off again. You can also set similar Wi-Fi connectivity rules, or only have web data enabled when you've got your screen on.
That's all in the free app — paying for UltimateJuice (€2.79) provides access to MMS messages, more automated Wi-Fi features, and a daily "night" sleep schedule. We've previously praised APNDroid for offering a similar on-off capability, but the app it plugs into for automation, Locale, now costs $US10.
JuiceDefender is a free download in the Android Market, with some features requiring a paid upgrade. For more tips on getting more life from your Android phone, and other smartphones, tip on over to our exhaustive smartphone battery guide.