JuiceDefender is one of the most useful applications out there in the Market for the great price of FREE. Of course, there is the UltimateJuice add on that adds more advanced configuration options but this review is going to focus mainly on what the free version offers, which is quite a lot already! Apologies for some of the "camera screenshots". It's too difficult to take screenshots on an Android! Functionality Android phones thrive on data. We get "push" features though the use of always on data connection via 3G or WiFi. Obviously, this causes a problem on the battery lifespan. JuiceDefender attempts to extend the life of your battery using several mechanisms to enable or disable APN (3G Data connections) and WiFi depending on several factors. I will use the term "data" to envelope both 3G and WiFi connections in the text below. Configuration on the software can range from as straightforward as simply "enabling" the application to head-scratchingly confusing for those who would like to venture into the advanced mode. I simply use the simple interface and I am rather satisfied with the result. I find that the UI can be signficantly improved to use the standard Android configuration menu instead. I think the most useful feature it has is the enabling of data every set interval (say 15 minutes) for a period of time (say one minute). This enable apps to "sync" with the servers and for push notifications to be sent in (mostly Google Apps). Push notifications will not be instantenous, of course, but a delay of at most several minutes in exchange for longer lasting battery life is worth it. JuiceDefender also offer other ways of determining when data should be turned off or not. By default, it will set your data to always on when your screen is turned on, and when it is charging. It will also enable data is there is traffic of more than 10 KB for the past 30 seconds. These options try to eliminate the problems of sudden data disconnection while using the phone. I must point out that this might cause some problems for several applications: most notably instant messaging apps. If your instant messaging app is left on and it does not transmit enough data for JuiceDefender to decide that the traffic is high enough, you may get disconnected. There might be other apps but I have not had the chance to fully test them out. Apps that do periodic syncing instead of relying on push notifications (like the official Google apps: Gmail, Calendar etc.) might have problems if their sync schedule coincides with the time when JuiceDefender decides to disable data. Most notably, I have seen this with the Facebook App with its syncing of notifications. I suspect this situation might improve with Android 2.2 Froyo when the Google Push API becomes accessible to developers and more apps are written to use the API. Perhaps an option in the application to toggle data on/off when specific applications run will be useful. There are some other options such as totally disabling data while you sleep etc but these are only provided with a paid add-on: UltimateJuice. I don't think these are really essential and the free version is sufficient enough. The app also provides a "log" for you to track when it enables or disables data. The "screenshot" also shows the "simply" interface of the application. Effectiveness Of course, if you do not have an always on data, this application is more or less useless to you. Effectiveness has been mixed as I have gathered from the forums so you might have differing experiences. Still, I would encourage you to try it out for yourself to see if it works. From the rating of this application on the market, it is obvious that it has been effective for a lot of people. On my end, I have seen my battery life improve noticeably. While I do not have hard data, the app claims to have improved my battery life by two times. (I have some problems with how it estimates such a figure. It seems too arbritrary to be accurate). Idle time on the phone has seen less drops in percentage of battery life. You can track your battery life over time in a nice chart with JuicePlotter, another app from the same developer. On the above "screenshot" from JuicePlotter, you can tell that with mixed periods of idle and high intensive usage, my phone's battery can last for about 20 hours. I expect that if I did not charge the phone, it could well last me another 12 hours or so on very minimal usage. Do note that your experiences will vary! On the app front, I don't have any problems (other than Facebook) with my apps syncing. HTC Weather still updates frequently and my push notifications for the Google Apps work. One thing that many users, including myself, have noticed is that sometimes, the data connection cannot be re-enabled after turning the screen on. The only remedy is to reboot the system. My guess is that this is either a bug with Android or the application. This does not occur too frequently so I guess this is still tolerable. Conclusion Pros: - For the price, it is extremely worth it. - Does its job well - A lot of customisation options. Cons: - Advanced UI is confusing and difficult to use - Causes problems with some apps - Mixed Results - Useless if you do not have always on data - Problem re-enabling Data sometimes - Battery life extension estimation via some arbritrary algorithmn that I am not sure if it is accurate or not Don't mistake the longer Cons list as an indication of a bad application! There just isn't much to say of the app other than it does its job well. I would recommend you to try it out and see for yourself if it works for you. Score: 8.5/10 Last but not least Two apps from the same developer I would like to recommend you to try out in conjunction with this app: - JuicePlotter: A useful FREE app to plot out your battery usage over time. Use this to see if JuiceDefender works for you. - UltimateJuice: This paid add-on will allow you to configure the app even further for those of you who like to have total control over the settings.