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My Galaxy S2 has always shown not more than 8 hours of battery life. This is with the stock ROM, as well as the recent 2.3.5 update and a rooted kernel. All the battery saving tips I've seen essentially boil down to 'turn off everything that made you buy the damn phone in the first place and use it only for voice calls like a dumbphone.' - i.e. disable 3g/EDGE/wifi/gps/bluetooth/screen brightness. Of the lot, I've done the following:

  • Screen permanently set to 10% brightness, i.e. the lowest.
  • Bluetooth/Wifi/GPS only on when needed, which isn't much (Couple of Foursquare checkins everyday).
  • Sync disabled.
  • Haptic feedback/vibrations disabled.
  • The 2 capacitative buttons are set to only glow in the dark, so during the day they are never on.

Yet my battery goes down like crazy, and if I don't carry my charger with me the phone can't even make it through the day. Is there a way to find out what apps hog the battery?

The battery usage graph and list of apps by battery usage doesn't really help; it only shows me the apps that I've run myself recently.

So is there anything else one can do to improve battery life, or am I resigned to carrying around a charger always?

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There are lots of battery tips questions here. Did you look at any of them? (I see a whole host of likely candidates on the right under "Related".) –  Al E. Sep 26 '11 at 11:22
    
That was exactly my point - if the solution is to turn off everything it negates the purpose of having a smartphone. And all the tips I've seen so far boil down to just doing this. –  Rex Sep 26 '11 at 12:13
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I'd recommend experimenting with other kernels. On my original SGS Vibrant the stock kernel gives me a full day if I don't use it, whereas my current one gives almost a full week without use (just syncing over WiFi). It's never less than a day unless I have the screen on for hours. –  Matthew Read Sep 26 '11 at 14:09
    
A larger "extended" battery may be your only solution if you're not willing to give up on functionality. Of course a thicker battery means a fatter phone, but function before aesthetics, right? –  Chahk Sep 26 '11 at 14:12
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In my Galaxy s2, the battery live about 24+ hours in normal use. The main causes of consuming the battery that I noticed are the high traffic on WiFi or 3G, playing 3D games, and lighting the screen for hours. –  Homam Sep 28 '11 at 7:16
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7 Answers

up vote 12 down vote accepted

I usually get by the day by carrying a USB charger since I always have my laptop or other computers around me. Some people get through by buying a second battery pack or a thick extended battery.

Any apps that syncs every 15 minutes is battery sucker, since it prevents the phone from sleeping. Syncing every hour or so shouldn't affect battery by much. If possible you should prefer apps that uses C2DM (i.e. push instead of poll). Many apps that polls for data have configurable polling frequency, try to have the same polling frequency for all apps or integer multiples.

For mailboxes that need to receive occasional urgent emails, don't use the stock Email client, instead use Gmail client or Exchange which uses push. If your email server supports IMAP IDLE extension (a push extension for IMAP protocol), you should use third party IMAP client, e.g. K9 Mail. However, don't use push for low priority high-traffic mailbox. You might be able to find a sweet spot for yourself by using two or more mailboxes for your high urgency and high traffic mailbox.

If you're rooted, underclock. Most phones have much more CPU than is needed for daily usage; underclocking will curb the phone to not go full power state unexpectedly, remember to restore the clock before doing CPU intensive activities (e.g. games) and to underclock it again afterwards.

I hope you know to disable Live Wallpaper. They're good for showing off, but not if you want your phone to last the day.

Secure the phone in your pocket. I found that my phone drains battery faster when in a tight pocket since the hardware button are often accidentally pressed which activates the screen and prevents the phone from sleeping.

In some custom ROM, e.g. CyanogenMod, the notification bar have power widget, which is handy for quickly enabling/disabling battery sucking features, e.g. GPS, 3G, etc.

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However, remember that in the end it's all a tradeoff:

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+1 for that colorful Venn diagram –  emaillenin Sep 29 '11 at 13:03
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There are two apps, Juice Defender and Woofi, which, when used together can dramatically increase the battery life of your phone. The idea is that if you don't need to be notified the instant that you receive a message via the internet, your mobile data doesn't need to be on all the time. Juice Defender (among other things) will disable your mobile internet, and then re-enable it at a specified interval so that your phone will check for new notifications. It does not affect text messages and phone calls.

Woofi uses your network location as a basis to disable and enable wifi, so that you only have your wifi antenna turned on when you are somewhere you can use it. If you are a control freak like me, you could also do all of this with Tasker. I have it set up so that when my screen turns off all internet connections are disabled until I turn the screen back on. Then if it does not connect to wifi within 30 seconds, wifi is diabled. It turns data on every 10 minutes to notify me if I receive an email.

I put a shortcut to enable/disable this on my homescreen, and my battery life almost doubled.

Finally, if you just flashed a new rom, your battery life will be bad for the first week or so, until the Dalvik cache and battery information caches are built up. You should notice a significant boost in battery life after a few days.

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didn't know that about flashing +1 –  KevinOrr Mar 30 '13 at 22:07
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Biggest battery-killer for me is being in a place with little or no cell signal and having the cell antenna on. The phone is constantly trying to connect with the network and it just sucks the battery dry.

When I'm at work I can't get any signal in my office, so I put the thing in Airplane mode. (I can't make or receive calls anyway, so might as well.) I easily end the day with 80% battery. If I forget to do that, I'm out of juice by early afternoon.

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Sounds drastic..I've also seen my signal waltz up and down while at work. The thing is, this is my first non Nokia phone, and my previous N8 still managed to last 15 hours or so at work, with email sync enabled. –  Rex Sep 26 '11 at 12:15
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Thanks for the answers, ZShakespeare, Al Everett and Lie Ryan :) It's true, the cell network signal is quite poor at work - that could be why it drains so fast. I've tried out all your recommendations and in the interests of others, I'm going to document what I did:

First, for unrooted users. If you don't have Tasker, get it - it's the most powerful task automation tool for Android, though somewhat aimed at power users. There's no free version(15 day trial) but it's worth every penny. (It's a little cheaper when bought direct from the developer instead of from the Market). I have already set Tasker to kill wifi and disable autosync when I enter my office. Now in addition, I've created a profile to turn off the data connection(EDGE/3G) when the screen is blank.

Next for rooted users - and this is where I see the most drastic power saving - by underclocking the CPU. I am using 2.3.5 and have experimented with 2 kernels - DarkyROM's SuperCore 2.0 and Hacre's Ninphetamine. The latter is a high performance kernel with voltage regulation features (SuperCore doesn't support changing voltages). I've installed SetCPU, and set it to downclock from 1200 MHz to 800, and reduce the CPU voltage to 975 mV (at 800 MHz, lowering further will cause problems). I've also set it to further reduce the clock to 500 MHz when the screen is off. By doing this, I got a boost of nearly 4 hours in battery backup.

Looking at this, I wonder why Samsung doesn't do the same thing in the 'power saving' mode that is available by default; not everybody would want to/be able to experiment with rooting their phone.

Finally, about syncing apps and email - I turn off autosync while I'm in office, and at other times I use the built in mail client to sync my gmail every hour. My office Exchange mail is sync disabled while I'm in office, and set to push mail at other times. I don't get more than a couple of mails a day during non office hours.

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I find Power Saving Mode feature pretty good, anything not being used is shut off but turned on when needed automatically.

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My battery woes are despite having the powersaving mode always on :( –  Rex Sep 29 '11 at 4:23
    
I work in a secure room that has cinderblock walls with poured concrete in the voids and a heavy mesh screen (like heavy duty chicken wire or chain-link fence) embedded in the walls, the door is steel - and security cameras too to add to the fun. It acts like a Faraday Cage but even with all that I can get a signal sometimes but yes it can certainly drain the battery. –  dghughes Oct 11 '11 at 4:20
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You've already turned most off the features and yet if it only gives less than 8 hours, chances are there is some hardware fault. Maybe in battery.

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Settings -> Location -> turn off like everything Root your phone and underclock :) Keep google

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