I'm a little uncomfortable discussing this topic since it's early and because I believe that a coming firmware update will improve matters. But I've received many questions about the battery life situation with Surface Pro 3. So here's what I've seen so far.

Microsoft claims you can get up to 9 hours of battery life while browsing the web. And at the Surface Pro 3 announcement about 10 days ago, Panos Panay more nebulously claimed that the device got "all day battery life." With the understanding that relatively few people sit in front of a computer typing away for several hours at a time without charging it, it appears that the latter claim, while open to some discussion, is honest enough. That is, for most people, Surface Pro 3 absolutely has enough battery to get through a typical day.

Of course, I work from home so testing this type of thing is a bit difficult. But I do judge a device's battery life by how I need to use it. And in many cases that means working on a plane between Boston and some city on the west side of the country, a trip of some 5 to 6 hours usually.

On some trips, depending on my mood or level of writer's block, I will split the time in the air between writing and watching videos. And in the past I might have used two devices for that: An Ultrabook or similar for work and a mini-tablet for entertainment. Given what I've seen so far, there isn't a cross-country flight long enough in which Surface Pro 3 couldn't accommodate either or both use types.

As with previous Surface Pro devices, I did test battery life while playing back videos back-to-back, and sometimes with some empty time between videos, where the device's power management configuration was left to its own devices. (More on that in a bit.) What I'm seeing is about 7 hours of battery life while watching only HD movies purchased (and downloaded) from Xbox Video.

By comparison, Surface Pro 2 was able to get between 5 and 7.5 hours of battery life, a bit of a wide range, though the movies I watched on that device were standard definition DVD rips. The first Surface Pro device hit 4.5 to 5.5 hours (usually closer to the former). This is nowhere near the consistent 10 hours of battery life I saw with the ARM/RT-based Surface 2 (also with SD content). But then it comes with an asterisk.

As it turns out, the Surface Pro 3 review unit I'm currently borrowing has a power management issue. Microsoft has pledged to fix this issue with a firmware update that I assume will arrive on June 10, which is the next Patch Tuesday, or at least before Surface Pro 3 becomes generally available on June 20. But I wonder if the issues I'm seeing are impacting battery life.

I've compared notes with Mary Jo Foley and a few of the others who are testing Surface Pro 3, and the symptoms are varied. But Surface Pro 3 is the first Intel Core-based machine to provide Connected Standby functionality, as I understand it, and this is most probably at the heart of the matter.

The way it's supposed to work is that Surface Pro 3 will act like a Windows device—that is, not a "PC"—in normal use. You open the Type Cover, tap the power button or whatever, and it comes right on. But if you leave it sitting there asleep for four hours or more, Surface Pro 3 will go into hibernation mode, and then an even deeper sleep. So the next time you open the Type Cover, nothing happens. And when you tap the power button, it comes on like a PC—slowly—instead of a device.

This sound wonderful in theory. But as it stands right now, none of that is consistent. I could be using the device and walk away for a few minutes, but when I come back, I have a hard time waking it up. Sometimes I press and hold the power button in order to just reset the thing and it comes back on, finally, but not in a cold boot; everything is the way I left it.

It's a bit maddening, but the worst part, I think, is that the battery life is actually draining when it's asleep. On some of my battery tests, I've been gone when the video stopped playing, so some amount of time has elapsed between the end of the video and when I return. And based on what I'm seeing, the battery life delta has been consistently "off" in such situations. Put another way, if I'm sitting there babysitting it—as you would if you were actually watching the movies—I see better results.

I expect this situation to improve. And of course, I'm traveling via plane to Colorado this weekend, so I will work on the plane and see how that goes, and compare it to what I saw on the train ride home from New York after the Surface Pro 2 announcement, where I also used only battery power.

By the time I write my review, I will have at least a few trips under my belt, but I will also need to provide a second battery life article after the firmware update hits.

One other thing: When I attempted to use the Surface Pro 2-era Power Cover with Surface Pro 3, I noticed the device recognized it only as a Type Cover and loaded those drivers. So the Power Cover was unable to work as a power source, which is of course the point. Methinks a coming update will fix that handily, so one could always use an existing Power Cover as a quick battery life extender on the road if needed. But with 7+ hours of real-world battery life, I don't think Surface Pro 3 needs such an accessory, at least for most.

So even with the power management weirdness, battery life is good, and it is certainly within the range of "all day battery life." It's not as long-lived as the battery life I've seen with Surface 2, and never will be, nor is it as good as a MacBook Air. But it seems like it's in the right place generally. And it can only get better.

I'm very curious to see what changes with that coming firmware update.