In my recent “Power to the Smartphone” entry, I talked about the biggest drains on Smartphone batteries.  In this one, we’ll talk about how this differs in PocketPCs.  Almost everything I said about Smartphones in the previous entry is also true on PocketPCs, so make sure you read that entry before this one.  Note also that, when I say “PocketPC” I’m really talking about “PocketPC Phone Edition” devices.  We still sell PocketPCs that aren’t phones, but they’re a shrinking market. 


One Man’s Fundamental…

There are two differences between PocketPC and Smartphone that I consider fundamental: touch and suspend.   PocketPCs have a touch screen while Smartphones don’t, and PocketPCs suspend while Smartphones are “always on.” 

Now “fundamental” and “important” aren’t necessarily the same thing.  You might tell me that PocketPC having pOffice is way more important than whether or not the device suspends, and I might not argue with you.  But, for a battery life discussion, differences in which applications come with the device aren’t all that relevant.


Touch: It’s not all that electric

The touch screen itself isn’t a very large drain on power.  It’s similar to a button.  When it’s not being pressed, it burns almost no power.  When it is being pressed, it burns some, but not very much.  There are much bigger fish to fry than the touch screen.

The touch screen’s big claim to fame when it comes to battery life is that it can cause other big power drainers to run.  For instance, if you leave your PocketPC on and put it in your pocket, your pocket might touch the screen and cause the backlight to turn on.  As you know from the previous article, turning on the backlight is huge. 

Most people suspend their PocketPCs before putting them away, but you also run the risk of having the device wake up in your pocket for a meeting reminder or something, and then not turning off because the screen is being touched.  The Treo 700w has a killer solution to this problem in the form of a screen lock.  AKU2 devices also have a screen lock, though they’re not as good as the Treo’s.  From both a battery life standpoint as well as a “hey, how did this contact get changed?” one, it’s generally a good idea to lock the screen.


Suspend: And in the darkness bind them

The biggest difference between Smartphone and PocketPC is what’s happening when the screen is dark.  On both, if you don’t use the device for a minute or two the screen will turn off.  On PocketPC, you can also make this happen immediately by pressing the power button.  That’s not the important part, though.  The important part is that, on Smartphone, when the screen is off, applications are still running.  On PocketPC, for the most part, they’re not.  From a power savings standpoint, this has advantages and disadvantages.

The main advantage is that it’s much harder for an application to drain your batteries on PocketPC than on Smartphone.  Apps can still do bad things, but they have to work at it.  On a Smartphone, the app just needs to keep using the CPU to drain the batteries.  On a PocketPC, the app needs to keep the system from suspending first, then it can keep using the CPU to drain the batteries.  It’s pretty easy to do that, so this isn’t much protection against malicious apps.  But it’s reasonably unlikely that they’ll do it accidentally.  That stock ticker that I talked about in the Smartphone entry wouldn’t have as bad an effect on PocketPC, since it wouldn’t run while the PocketPC is suspended.

That’s the good news.  The bad news is that, if you don’t have apps that use the CPU when they shouldn’t, then suspending is actually worse for your battery life than not suspending.  Check out the “Mike, what are you smoking?” section of this entry if you’re interested in why.   The extremely short description, though, is that waking up and suspending again on a PocketPC takes a lot more time (and power) than doing the equivalent on a Smartphone.  This is no big deal if you’re just turning the device on occasionally to check your calendar.  But, in today’s highly connected world of devices that frequently download new mail and get SMSes, etc, the Smartphone model starts to really win out. 

The other downside is something of a secondary effect.  When PocketPC suspends, it specifically tells every driver to power itself down.  Because the PocketPC spends the majority of its time suspended, an OEM driver writer might be tempted to not do much power management in the driver itself and just rely on the suspend to take care of it.  On a Smartphone, however, the drivers have to aggressively manage their own power as quickly as possible, since they can’t rely on the big hammer that is suspend.  The end result is that, depending on the drivers, when the system is awake, it may be burning more power than an equivalent Smartphone would. 

So, what can a PocketPC user do about this?  Your job is to get the system to suspend as soon as possible.  Don’t wait for it to time out.  Press the power button when you’re done using it.  Be careful with apps that specifically keep the system awake.   For instance, if you use pMSN and sign in to IM, the device won’t suspend, even if you press the power button.  If you need to stay signed in, that’s what you need to do.  But be aware that it will affect your battery life.  If you’re syncing every five minutes, but reading mail every ten, consider syncing less often.  Etc.


LCDs and Other stuff

The other stuff is important, but maybe obvious.  PocketPCs tend to be physically larger than Smartphones, so they often have the ability to have larger batteries.  On the other hand, they also tend to have physically larger screens that need bigger backlights which burn more power. 

There were a few questions regarding LCDs in the comments of the previous entry.  I’ll try to answer them here.  So everyone is on the same page, when I say, “LCD” I’m talking about the screen but not the backlight.  Also, what I say about LCDs is the same for PocketPC and Smartphone.

One question was why black and white LCDs burn less power than color ones.  The main answer is that every dot (pixel) on a black and white screen takes one transistor, while every dot on a color screen takes three.  Transistors burn power.  Also, color screens tend to have more pixels than black and white ones (they’re higher resolution).  And, since there are more pixels in the same space, they tend to be packed more tightly together.  That means that you need a brighter backlight to shine through the tight mesh of them.  Finally, because pure black and white is high contrast, you need less light for your eyes to see it.  Some black and white external screens (like on a flip phone) don’t even have backlights. 

There was also a question on whether choosing a dark or bright background has any effect on power.  On a big LCD screen, it really doesn’t.   On some LCD technologies, it might have a small effect.  For instance, if you think about the black and white LCD on a calculator, when it’s not showing anything the screen is “white” and when it’s showing numbers, those numbers are “black.”  Not showing anything probably burns a little less power than showing something.  For a color LCD, though, there’s little, if any, difference between black and white.  However, there’s an upcoming technology called “OLED” where black doesn’t burn any power and white burns power.  So, depending on the technology, we’ve got black background being better than white, white background being better than black, and it not mattering.  Confusing?  The good news is that none of this matters.  The amount of power the LCD uses is completely insignificant compared to the backlight, and there aren’t many hours out of the day where the LCD is on but the backlight is off.

I hope these articles have answered your questions about PocketPC and Smartphone batteries.  As always, if you have more, ask away in the comments section.

Mike Calligaro