The iPhone 4’s battery life is legendary, and my wife’s experience certainly bears that out. In any event, I was worried that my Captivate would not fare as well: a few posts on XDA Forums, while helpful as usual, did make me a bit nervous.
Well, all I can say is that my fears were unjustified. For my purposes at least, the Captivate’s battery life is not just adequate, but excellent. However, I have learned a few things about battery management that may be useful to share. First, though, I think no useful discussion of battery life can be had without information on actual usage patterns; so, here’s mine (on work days).
- Unplug the phone around 8am
- On my way to the kids’ school and work, make a few phone calls using Bluetooth, for a total talk time of maybe 15-20 minutes on average
- Sometimes also listen to music, plugging into my car stereo’s AUX input.
- Make perhaps 1 or 2 phone calls during the work day
- One 10-15 min phone call home while on my way back from work
- In the evening, play a couple of games (well, either I or the kids almost always do), read a book using the Kindle app, check the Android market for updates, check email
- Plug in the phone around 11pm
So, overall, I’d say my usage is lightish, but not conservative. Depending on how hard I / we play in the evening 🙂 and the duration of calls made during the day, I usually have between 20% and 60% battery life left by the time I plug it back in.
In fact, when the battery life is above 50% in the evening, I do not plug the phone in; I disable syncing and put it in flight mode. So, I sometimes manage two days on a single charge. This is often the case on week-ends, when I use the phone more for surfing, email, maps/navigation and games, and less for actually, well, making calls!
With that out of the way, here are my own conclusions about battery life.
First, voice calls and your display are the main source of battery drain. It’s that simple. You can see for yourself: go to Settings, About Phone, Battery Use. This means that, when you are optimizing battery life, you are really nibbling at the edges: the first-order sources of power drain are essentially unavoidable. Then again, in my experience, if I restrict attention to making phone calls, the battery life I get is comparable to what I got out of my trusty old Nokia 3500: not too bad, but rarely beyond one or maybe two days of actual use.
Second, turning GPS and WiFi on only as needed makes very little difference. This was a surprise to me, but I spent a few days recording the battery level at roughly one-hour intervals with GPS and WiFi both off, and with GPS and WiFi both "formally" on (more in a sec). In either case, I lose about 2% charge per hour while idle; the phone may discharge marginally faster (between 2% and 3%) if GPS and WiFi are both on, but the difference is so small that, honestly, you would need much more careful measurement, and more extensive tests, to be really sure. If there is a difference, in my opinion it is more than compensated by the fact that you don’t have to turn on these services as needed
Actually, this makes sense. The GPS radio is only active when location is required, as you can see by checking the notification bar. Similarly, WiFi is placed in an energy-saving "sleep" state when the display is off, so again there is no significant drain, unless you use the phone. In principle, you should get a higher drain with WiFi on than with WiFi off, given equal functionality, if you use the phone, say, for surfing the Web via 3G while in an area with no accessible WiFi; in such circumstances, the phone keeps looking for a WiFi signal (and an access point that has been used in the past), so turning WiFi off would save some power. But, again, in my own actual use, this does not end up mattering much, so I just leave WiFi on at all times.
Third, syncing does make a measurable difference. If I leave syncing on during the work day, the phone discharges at a rate of maybe 3-4% per hour, vs. 2% with syncing off. Basically, this is due to K-9 (my favorite email client by far) polling my employer’s IMAP server every 15 minutes, and GMail’s push service. Again, the difference is not huge, but I also find it a bit annoying to hear the "new mail" sound every 15 minutes while I’m staring at my iMac in any case. But, syncing is the only setting that I found to have an easily noticeable effect on battery life. To turn it on and off, I use the Autosync Toggle widget from Curvefish, which I find aesthetically pleasing.
Fourth, you will have background data traffic even with syncing off. This is especially important, and (in my view) an Android limitation. Only certain services, such as checking email in the background, qualify as "autosyncing"; for instance, GMail checking. You can check what these registered autosync services are by going to Settings, Accounts and Sync. In addition, email software such as K-9 has a setting that enables background polling only if Autosync is enabled. However, not all background data is considered autosyncing; for instance, the Beautiful Widgets weather display is updated even with syncing off, as is the Facebook widget. I am quite sure there are other data services that are active even with syncing off. To kill these, you have to basically stop all data traffic. The Captivate (with stock 2.1 Android) does not really have a fully functioning data on/off widget, but you can dial the "secret code" for testing mode, *#*#4636#*#*, and disable data off from there. Confusing? Yes, it is! But, for now, this is what we have to deal with on Android.
Turning all background data off does reduce power drain, but the real reason why I mention this is that getting into Testing Mode as just described is the only sure-fire way to avoid data charges. Again, turning syncing off won’t do, and of course going to Flight Mode prevents you from making and receiving phone calls. Case in point: before I bought a suitable Vodafone IT SIM card with reasonably priced data service, I had a voice-only plan that happily charged me a 0.50 EUR per 15-minute session (or something outrageous like that). And, since it,too was a Vodafone IT plan and I was in Italy, switching Roaming data off obviously made no difference. So, again, Testing Mode is your friend if you absolutely must avoid data. BTW I understand that HTC phones, as well as the Captivate and other Galaxy S phones with the as-yet unreleased Froyo, do have a data off switch, but there is no such functionality with the stock 2.1 firmware.
Finally, two tips: if you leave your phone in flight mode to save power, do also turn syncing off; it seems to make a difference. Second, to check battery life, I recommend Battery Indicator Pro. It displays the current battery level numerically in the notification bar; you can get additional information if you pull down the notification bar and tap on the Battery Indicator line. There is also a free version, but you do want to support Android developers, don’t you?