While I had hoped to quickly assess the impact of the new Surface Power Cover on each supported Surface mode, battery life testing is of course time consuming and difficult. So rather than make you wait, let me cut right to the chase: If you own an original generation Surface Pro, the Power Cover isn't ideal, as it adds weight and bulk to an already heavy device. But it's the best way to achieve reasonable battery life on a device that falls very short in this important category.

If you go back and check out my review of the original Surface Pro, you'll see that while I liked the device overall, it got dings for its heaviness compared to Surface RT—"the device seems, well, denser for lack of a better term," I wrote—and less-than-stellar battery life. Surface Pro 2, which shipped a scant 8 months after the original version, was an evolutionary update, as I noted in my review of that device. It did absolutely nothing to improve on the original's weight, but thanks to the Intel Core "Haswell" processor, battery life was up dramatically.

How dramatically? Where the original Surface Pro could wheeze out 4, maybe 4.5 hours of useful life from a charge, Surface Pro 2 averaged about 6.25 hours of life in my own admittedly unscientific tests. That's not stellar in age in which any reasonable Ultrabook can achieve 8 to 10 hours of battery life, if not more. But it's the difference between non-starter and passable.

This change, plus a few other niceties like the dual-position kickstand, makes the Surface Pro 2 a better deal than its predecessor. But that doesn't help the many people who purchased the first generation unit.

And that's where the Power Cover comes in.

I'm not going to retread ground here. Check out my Surface Power Cover First Impressions and Photos for all the basics about this accessory.

Problematically, Power Cover of course adds weight. 1.2 pounds to be exact, bringing the curb weight of your Surface Pro up to a surprisingly imposing 3.2 pounds. That doesn't sound bad, right? After all, the waif-like ThinkPad Carbon X1 (2014) that I'm currently reviewing weighs just .3 pounds less than that. But that weight is packed into a smaller, thicker and denser package. And it really does feel much heavier when you do a side-by-side test.

Obviously, nothing is going to fix the fact that the Surface Pro is heavy and thick. You knew that when you bought it, and it is what it is. Another way to think about this is that the Power Cover is about the same weight as two Type Cover 2 typing covers. And Type Cover 2 isn't heavy at all.

What everyone really wants to know is how the Power Cover impacts battery life. At the Surface 2 launch last September, Microsoft provided contradictory information about this, and depending on where you look today, it's still hard to know where things stands. Here's the official word: It varies by Surface model. And on the original Surface Pro, Microsoft says the Power Cover should improve battery life by about 70 percent.

So get ready for the shocker. It does (almost) exactly that. In repeated tests in which I played back exactly the same set of movies as I did with the original Surface Pro (ah, the power of keeping good notes), I saw a 68 percent improvements in battery life on average.

What is that in the real world? That's an average of 6 hours and 35 minutes. My average on the original Surface Pro was 4 hours and 30 minutes.

A few notes.

When you run down the batteries, the Power Cover battery is used first, and the internal battery is not touched until the Power Cover drains. This makes plenty of sense.

When you charge the two, the internal battery charges first, and then the Power Cover. This also makes sense.

During the first couple of rounds of testing, I used the Surface Docking Station to charge both devices. I usually use the Dock with a Surface Pro 2, but I figured this would give me the best performance from a charge time perspective. Oddly, it does not. After charging the combo overnight twice, I awoke to discover that the Power Cover was nowhere near charged, despite the fact that it had been plugged into power for at least 8 hours. That is obviously unacceptable. But in charging the device with the Surface Pro's normal charging cable, overnight charges worked as expected. I'm not sure if I'll ever be able to explain what happened there, but I wanted to at least point it out.

It doesn't included backlit keys. This will bother some, and certainly I'd prefer it, at least as an option.

Some will argue that the Power Cover is expensive. And certainly, $200 is nothing to sneeze at. But in my estimation, if you have made a $1000+ investment in the original Surface Pro and wish to prolong your use of this device another year or two, the resulting battery life gains make this decision a bit easier. I've not yet tested Power Cover with Surface 2 or Surface Pro 2, but Microsoft tells me the battery life addition will be more modest. More to the point, it's less critical on those devices as well. But you either need the additional life or you don't.

The way I look at it, few people will purchase a new Surface Pro 2 or Surface 2 and a Power Cover at the same time. But this accessory makes plenty of sense for those, especially those with an original Surface Pro, who have used their device out in the world and simply require more juice.

I'm a bit weirded out by the Docking Station charging behavior and can't explain that. But since it seems to work fine with the bundled Surface Pro charger, and will prolong the life of your original Surface Pro, this accessory makes plenty of sense. Recommended for original Surface Pro users, with the usual caveats.