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Understanding your HTC EVO battery (or why I scream mAh!)

Android Battery by xioubin lowEver wonder what's draining your battery, or how long your battery should last? Curious about why your battery lasts longer on cooler days, or why a fully charged battery lasted ten hours yesterday and died in six today?

How can you run your HTC EVO 4G for 12 days without a charge? How can you get 230% more life from your HTC EVO 3D?

Well, I'm going to attempt to answer these questions and a bit more. I'm not an electrical engineer, so if I got something wrong, please let me know and I'll fix it.

What can my battery do? How much gas is in that thing?

Every HTC EVO 4G came stock with a 1500mAh battery, while the HTC EVO 3D came with a 1700mAh battery.

To understand how much juice is in those things, you should know that that mAh means milliampere-hour. A 1500mAh battery can produce 1.5 Amps of electricity for one hour. Were we to look at this in lightbulb terms, a 1500mAh battery would theoretically power a 60 watt lightbulb for about three hours, or your phone for around eight on average.

This isn't the end-all estimate of how much power you've got in your hands, but it's a decent starting point. For those interested, watts = volts * amps. 120 volts is standard from USA wall outlets.

You can purchase larger batteries for your phone and generally assume a 3000mAh battery has about the power of two 1500mAh batteries. Things do vary a bit (which I will go into later), so your results may exceed or fall short of what you expected.

How much am I using?

While not flawless, Battery Monitor Widget is a pretty darn useful tool to see minute by minute how much of a drain on that gas tank you're pulling. It has some neat prediction options to tell you when it thinks your phone will run out of gas, too, but that varies depending on what you're going to do with it.

But it lasted so long yesterday…

Your phone starts fully charged, sitting on the desk at work for six hours between 8 a.m. and 2 p.m., yet each day at 2 p.m. the amount of juice left is different. The factors behind battery consumption are how many programs are eating CPU time, what radios are on, what the conditions are between your phone and the cell tower (are there 40 people on that tower or 4000?), the temperature of the battery (hot battery loses juice), and the age and condition of the battery. Did you get a lot of email today that synced in the background, and was the server quick or slow in responding?

While hard to believe, moving from one room to the next can significantly raise power consumption by your phone too, as now you have to blast through your walls to get a signal out to a tower.

How long can this battery last?

For an experiment on the EVO 4G, I ran a Seido 3500mAh battery for over 12 days and still had 20% battery life left. This is something you can claim, and although true, it's completely misleading. On a standard day that battery had 24-36 hours of life in it, and on a heavy-use day about 12-14 hours.

I ran for 12 days in airplane mode using GrooveIP and WiFi only and never turned the screen on except to see what the percentage of battery left was. Estimates said it would have made it to somewhere around 15 days without a recharge, but I had things I had to do.

Does this sound like your normal use? No. Not a chance you're going to reach that with these phones and normal use.

Applications like Angry Birds, Wind-up Knight, and any of the Zynga apps I've played with use tons of juice when they are running in the foreground. Other apps don't use much. App power usage is usually defined by graphics and data read/written over the air.

I did the math, I followed my usage, and it died before it should.

If a battery advertises 1000mAh, that's probably what it's capable of, but you're likely not going to get it. Think of a motorcycle that is capable of doing 160 MPH; you can do this, but if you do it all the time, the engine is going to break down and wear out quickly. A battery completely used from full charge to nothing will wear out significantly faster than a battery used at about 90% charge to 15%.

Most batteries have governors that prevent them from getting too charged, or too empty. So you're looking at perhaps using 80% of your battery since the manufacturers do not want a battery that could last for three years returned in a month for being dead.

If it's hot, your battery may not produce electricity as effeciently.

What about underclocking?

CPU speed lowered 50% = total power savings of 50%? No. Your CPU is just one component that draws power. Your screen, cell radio, WiFi radio, 4G radio, IO operations, speaker, camera, and LED notification lights are others.

Underclocking saves battery, yes, but clock speed is just a piece of the battery drain puzzle.

Okay, then what about undervolting?

The theory here goes that since watts (total power used) = volts (frequency) * amps (power), lowering the voltage to the CPU will use less power. I'm not going to say it doesn't work. In theory it should.

I've run plenty of undervolting kernels and noticed when I undervolt too much, the properly clocked but undervolted CPU slows down slightly. So, your time to load that web page or application may take a little longer, meaning the screen is on just a little longer, meaning more power draw. It can work, and it can be great in idle situations, but your results will vary.

I need some battery-saving app recommendations.

The simple fact is these kinds of apps work by making your phone not work.

Juice Defender is one of my favorites. It achieves great improvements in battery life by limiting when your apps can request data and turning off radios based on various conditions. The downside of this is that your previously up-to-the-second smartphone can become an "oh yeah, 15 minutes ago this happened" smartphone. In a lot of cases, you can see similar savings by simply disabling auto-sync.

Task killers are touted as another juice saving application. The theory goes that tasks in memory take juice just to be there and that if they're in memory they'll probably use the CPU and the memory manager will have to work around them. Sounds reasonable.

But imagine this scenario: you load up your fully-automatic task killer and set it to kill anything you don't know. BAM! All gone, but that one app just reloaded. No problem. BAM! again and that app is down again. Oh wait, it's rising again as it's supposed to? BAM! again. Each and every time the app rose it took hundreds of thousands of IO operations, CPU calculations, memory management operations, and so on to do that. You can burn your battery through just wasting juice trying to kill a zombie process that would otherwise sit in your phone's memory peacefully.

What's this SBC/trickle charging I keep hearing about?

Trickle charging works wonders by stuffing some more juice in your battery. It charges closer to the limits of the battery, then maintains the top off charge.

Upside: you get more life. Downside: some people claim the different charging method caused their batteries to explode. The newest HTC kernels are evidently trickle charging.

How much do the radios drain my battery?

People suggest turning off WiFi when you're not using it actively. If you're near it I say leave it on.

It might help to think of your EVO as yourself, and the reciever you're talking to as another person for this. How loud do you have to speak (juice do you have to use) to talk to the other person? If it's WiFi, chances are you are very very close to them and can whisper. It does not take much effort to get the message there.

If it's 3G/4G, you're yelling up to a couple of miles to someone else. Sometimes they can't quite hear you and need you to repeat.

Running a radio and not transmitting much data across it does not cause a significant drain of the battery. If you use your WiFi even just a few times to move data (background email sync, twitter/Facebook update, etc.), you'll probably save out in the end.

I should keep GPS off when I'm not using it, right?

The GPS toggle on your phone turns off the ability of a program to locate you within 15 feet, but it does not save battery. GPS is passive. It only starts draining resources when it's activated by a program like Google Maps, Facebook Places, Sprint Navigation, Foursquare, or Yelp.

The GPS receiver radio also does not draw a heck of a lot of power when it's turned on, but GPS processing does (at least that's what I'm lead to understand). Trying to triangulate a position based on 3-7 satellite ping times without knowing your altitude takes a lot of juice to process. Oddly, new phones are coming out with barometers to solve some of this processing drain and get faster locks.

Does recording in 3D use more battery?

One camera = x power drain when on. Two cameras = 2x power drain. 3D = 2x+? power drain.

When you're taking 3D video or pictures, your second CPU core is in full swing, your GPU is at full tilt, all sorts of battery draining things happen when you're in 3-D picture or video mode. If you've got GPS tagging on, your GPS also just kicked into high gear.

Mmmm, your battery life tastes sooo good.

Programs running in the background are bad for my battery, aren't they?

Just because a program is in memory does not mean it's actually running. Some programs are loaded and just sit there on the chance they will be needed. Android, and most other things these days, is an event-driven operating system. There's no need for Clown.apk to do anything, even if it's in memory, until the Scared_Child process calls it.

You can see program's battery usage with the OS, but you might want to grab something like System Tuner to see how many clock cycles it used in addition.

What are some things I just can't control?

It would be nice if we completely controlled our battery life, wouldn't it? That way, we could claim extreme numbers, actually prove it, and then be the battery life winner. Unfortunately that's not the case as you, your phone and programs, and your battery are still not the entirety of the equation.

Last year there was a snowstorm where I live. Thousands of people suddenly were trapped on the roads within two miles of me, and my radio drain went through the roof as it was screaming to the tower just to be heard.

Earlier this year I noticed I only had two bars of signal at home. Considering the tower is visible across the street from me on a building, this was kind of odd. I grabbed a tower location program from the Market, and sure enough I was not using that tower. I rebooted my phone and experienced the same issue. An hour later, there were people working on the tower.

When it's snowing or raining, my signal degrades.

If your team's on a winning streak, forget battery life for miles around during gameday.

New game grabbed your attention? Okay, you sort of do control this one…

Near water? Power outages miles away. Telephone poles down. Internet slowdowns behind the tower causing your requests to take longer. Sunspots and solar flares. Airwave interference. Hostage situation down the street. Old phones nearby. Someone using all the bandwidth. Ambient temperature causing issues with the cell tower, your battery, the cell phone spectrum we use.


That's about it.

There's no magic button for great battery life. There are some tips you can use to improve battery life, but you're not going to see multi-day improvements without purchasing an extended battery and changing your habits.

If you want to know everything about your battery, check out Battery University, which I am obviously not a graduate of. 

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Paul E King

Paul King started with GoodAndEVO in 2011, which merged with Pocketables, and as of 2018 he's evidently the owner. He lives in Nashville, works at a film production company, is married with two kids. Facebook | Twitter | Donate | More posts by Paul | Subscribe to Paul's posts

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