read the review quite useful but found that some function is stupid...
JuiceDefender
Amazing phones with little juice
Wanna save battery? It’s easy!
Being online at any time and any place is what smartphones are all about. Yet this continuous connectivity is quite power-hungry; as a consequence, modern smartphones are plagued by sucky battery life.
JuiceDefender is the solution: it intelligently and transparently manages for you mobile connectivity and other battery-sensitive components. Be online when you actually need it - save battery when you don’t!
The default Easy Mode is a no-fuss, one-click way to have your battery last longer - much longer. Just enable JuiceDefender by tapping on the Big Button™ and you’re ready to go!
If you want more fine-grained control, Advanced Mode will let you configure all of JuiceDefender’s features to your liking.
Complete, automated control
JuiceDefender can control on your behalf
Should you Download JuiceDefender? Yes! Must Have Android App! [Android Tapp]
JuiceDefender is an app that you won’t believe you lived without. You will be impressed by the amount of battery that you actually save, and might even consider buying the paid version! >[Best Android Apps Review]
I went from 16 hours of use to 48 with a Nexus One. […] I wholeheartedly recommend this killer, beta app. [DroidDog]
Can’t get much better than that. [designerati daily]
For a free Android application, JuiceDefender offers quite a number of impressive battery-saving features. [Daily News 1001]
For Android users I highly recommend JuiceDefender: use the juice when you need it, save it when you don’t! [lo-ga-rie]
Besides the battery savings, those who like to parse out their email checks and avoid minute-by-minute distractions see some benefit here, too. [lifehacker]
* Mobile Data - the main ingredient in the recipe for effective battery saving, JuiceDefender can enable and disable Mobile Data for you, following the rules you specify (see triggers below); this also works on Verizon and Sprint (CDMA) phones!
* 2G/3G toggling - automatically switching to 2G only when your phone is not in use can save a ton of juice! (only available on certain ROMs due to Android limitations)
* the WiFi radio* - another slow but steady battery drainer; why keep it powered all the time when it’s only used occasionally? The Location feature (see below) is particularly useful for fully automated WiFi management
* screen off/screen lock timeouts* - modern, large smartphones screens drink your precious juice like there was no tomorrow; it’s important to have a short auto-screen-off timeout interval, but having to enter the unlock pattern/pin every time becomes quickly annoying. JuiceDefender lets you specify a longer timeout interval for locking the handset, thus keeping you sane and your phone secure.
* minimum and maximum CPU frequencies* - knock down on your thirsty CPU’s juice consumption while the phone is sitting idle in your pocket; unleash its full power the moment you start using it (only available on certain ROMs)
*requires UltimateJuice
There are a number fully configurable triggers that interact together to automatically control your handset:
* Schedule - the heart of Juicedefender! It can keep the connectivity enabled or disabled all the time, or enable it briefly on a regular interval (every 5 minutes to 2 hours), to let background data sync occur (email, Twitter, Facebook, stock quotes…) A schedule interval of 15 minutes is sufficient in most situations; a longer one is useful to minimize distractions when you need to get something done

* Night* - keep the connectivity disabled during the night; you can also have it enable Silent Mode or, for even greater battery saving, Airplane Mode.
* Battery - disable the connectivity when the remaining battery charge goes below a specified percentage
* Traffic - keep the connectivity enabled while there is an ongoing data transfer; this makes sure that syncs (or large downloads/uploads) are completed successfully.
* Apps - select which apps are allowed to keep connectivity enabled (Pandora, last.fm, online radios…) and which ones will disable it (games, ebooks, offline reading…)
* Screen - keep the connectivty enabled while the screen is on to allow browsing, tweeting, procrastination and generally internet-powered enjoyment
* Location* - automatically keep WiFi completely disabled when not in range of known WiFi networks
*requires UltimateJuice
The main UI in Advanced Mode (click to enlarge)The UI shows how each trigger will behave with the current configuration, following their priority order (lower-priority triggers are listed first).
Most triggers have further specific options; for example the Screen trigger can be enforced only after unlocking the device (so that you can glance at the time without wasting a drop of juice), and it can be set to be ignored when the battery is low, effectively changing the triggers’ relative priority.
And there’s more!
JuiceDefender is designed to work in a completely transparent way; once you have configured it properly according to your needs it won’t interfere with your normal phone usage. You’ll only notice it’s there at bedtime, when you’ll realize you still have plenty of battery left!
However if you want to keep an eye on its operation (especially useful during the initial configuration phase) you can enable the notification - the current status of all controls and triggers will be always available in the notification pane.
It also comes with a couple of useful Home screen widgets:
* the Toggle mobile data widget lets you quickly force-enable or force-disable mobile data with a single tap, if you need to override JuiceDefender’s control (it has the highest priority)
* Widgets!the JuiceDefender widget shows an estimate of how much battery life was improved by JuiceDefender over the last 48 hours - what’s the best multiplier you can get? It also lets you enable/disable JuiceDefender super-quickly; just tap on the glass of juice.
Want to know more? Check out the FAQ and the changelog or head over to the feedback/support forums!
Reclaim your battery
Some features are not available on the free JuiceDefender - but what’s there is enough to considerably improve your battery life, for free!
Way-over-the-top promo banner, 90s style (hey, at least it doesn’t flash!)
To get complete control over your handset’s juice consumption consider purchasing UltimateJuice from the Android Market or AndAppStore. It’ll enable WiFi, Timeout and CPU control, unlimited Apps, the Night, Peak and Location triggers and all Schedule intervals - it will make your battery last forever! (ok, that’s a hyperbole)
in some review it said keep data off when the screen when to sleep and on back when you reactivate it when you on back... that is stupid when u need push emails totally disable the pushing... but you can tune it a lil here and there... will tryout and let you guys know... but not that fast already coz i'll go SG for 2 days so wednesday only can try on my regular usage...