I looked at my phone at about 9:30 p.m. last night. Battery level: 21 percent. My wake-up time these days is 5:30 a.m., so 21 percent would do. This thing used to give me the 10% warning every day at around 3 p.m. So I poured some Jim Beam Single Barrel over some ice, and quietly toasted the end of a very long journey.
You see, I have been thinking, talking, tinkering, obsessing, advising, and researching battery life for as long as I've had a smartphone–at least 5 years. I've dialed down GPS accuracy, messed with non-push Gmail, set up complicated on/off switches with Tasker and Trigger, rooted my phone, and generally spent far too much time under the hood, when what I really want to do is drive the thing.
Then a few weeks back, while browsing for something else entirely, I found this little Android app, Lux. It runs in the background on your phone and, essentially, takes over the brightness level. It's very smart on its own, but after a few "training" sessions, it knows exactly how bright your phone display should be: in a pitch-dark bedroom, in direct sunlight, at your well-lit office, and everywhere in-between.
But first, a word about your smartphone's display: it gobbles battery life. It wolfs it down like a marathon runner taken from the finish line to a donut shop with great iced coffee. Rhett Alain wrote a beautifully graph-y post for Wired about how brightness affects battery life. That post says, very explicitly, yes: Decreased brightness increases your phone's battery life, in a way you will notice. With all credit due to Alain and Wired, the key graph from Alain's iPhone 4 tests:
And the key text, which considers another big factor (data transfer) played against brightness:
An iPhone 4 should last about 6.5 hours of continuous use on the lowest brightness setting and about 3.5 hours on the highest brightness setting. That’s a pretty big difference. It seems putting the brightness at about half would give a fairly reasonable time of around 5 hours. Remember though, this is with wifi and 3G off. So, really your phone wouldn’t even last that long. I think it is safe to say that you will still get more battery time from your phone at half brightness than at full.
"But," you say, "my phone automatically changes its brightness." Sure it does, except your phone sucks at being reasonable with lamp power. It's understandable, when you think about how phone makers want their expensive, competitive screens to look: bright and crisp. Except that you can't see anything on a phone that is out of battery power, and keeping a sensor active to monitor ambient light around you itself eats up some battery power. Note, too, that the smoothness and accuracy of automatic adjustments vary from maker to maker.
We come back to Lux, which is free in its "Lite" version, and is worth at least a try (and an upgrade to the full version, too, if you see the results I see). After you install it and launch it, Lux will walk you through the setup process. It is not the most informative and plain-English tutorial I have seen, but accepting all the defaults will, at least for now, get you where you need.
Lux wants to keep itself constantly active in your notification tray, and you should let it do that. It might seem a bit annoying at first, but giving it that power allows Lux to fully do its job of watching and ajusting brightness. More importantly, you can access Lux with a quick flick of the notification try, so you can quickly adjust brightness up or down 20%, or make more drastic manual adjustments.
From then on, you have a small job that will be over after a few days: turn on your phone in different kinds of light. This shouldn't be hard, because most of us are too easily bored and distracted. If your phone is too dim or too bright, tap on Lux in your notification area (which you pull down from the top of the screen) and slide the brightness until it's just right. Then tap and hold the little "link" icon in the middle of the Lux pop-up to link this screen brightness to these conditions.
The How-To Geek site has a much more detailed tutorial on setting up Lux. But for the most part, the default settings are fine, you don't need to touch anything except the brightness slider and the "link" button, and you'll start getting smarter brightness and better battery life. Over a few weeks, I've taught my HTC One that my eyes are good enough to use a lower brightness for most conditions (pictured below).
You would think that having a light-watching app stay awake and adjust the brightness would have the opposite effect on battery life, but look again at those battery/brightness tests: you can nearly double your battery life when you don't make it power a lamp all the time. Lux has made a huge difference in the battery life of my HTC One (the M7/2013 HTC One, that is). My phone can make it into the evening without a mid-day charge, and I can see unnecessary emails and tweets just fine.
The only more effective way I know of to improve battery life is to stop looking at your phone so often. But our session is up, and I'm not actually qualified to hear about your childhood and sense of being needed and procrastination and so forth. Just ... just try Lux for a bit. And reward yourself when you make it a full day.