Compared to an ARM processor, the battery life of a PC with a Core i5 in is always going to be disappointing. Initially Microsoft said its Surface Pro would have half the battery life of the Surface RT, around five hours instead of 10.
As usual, whether that's accurate depends what you're doing. On our rundown tests, which keep the screen on and the CPU and GPU running continually, with Wi-Fi and background tasks running, we could run the battery down in a little less than three hours.
But our test is designed to hammer battery life, and you're rarely going to run anything that demanding in real life for as long as it takes to run out of battery.
With the screen at a comfortable brightness for working next to a large window, running multiple desktop programs and Windows Store apps at the same time, with Wi-Fi on and the USB port in use, browsing the web and receiving and sending email, we were routinely able to work for over eight hours.
Adding in the times when we walked away to get a cup of tea or made a phone call and allowed the Surface Pro to go to sleep, on one occasion it was almost 10 hours from unplugging the power to seeing the warning that the battery was so low the system was about to hibernate.
Depending on what you do, this is going to vary the way it does on any other notebook; play movies or browse web pages that use the GPU more, and you'll get shorter battery life. Turn off Wi-Fi and turn the brightness down and unplug USB devices and you'll get longer battery life.
And as you do different things, the predicted battery life will go up and down, just as on any other Windows systems.
So 10 minutes of running demanding browser rendering benchmarks with 55% charge left Windows predicting under an hour of battery life if we kept on running the test. Closing the browser test put predicted battery life back up over two hours, and we were able to carry on working for longer than that in the end.
Think of the Surface Pro as an Ultrabook that just happens to look like a tablet (rather than a heavy iPad that runs desktop applications, say) and it has better than usual battery life.
When you do need to plug it in, the charger for the Surface Pro is a bit bigger than the Surface RT charger, although it's the same neat shape, just with a short, flat power cable.
The extra size is needed to pump out more power, and means that even though Surface Pro needs about 44W instead of the 24W that charges Surface RT, it still charges completely, from flat, in under two hours. In just an hour's charging we were back up to 85% battery life.
Handily, there's also a USB port on the charger, so you can plug your phone, camera and other USB-powered gadgets in to the same charger, which saves space when you're travelling.
If you already have a Surface RT, you can use its charger for the Surface Pro in a pinch. It doesn't charge as fast, but it still charges, which is handy for topping up at home if you keep your Pro charger at work, for instance, or if you don't want to go all the way downstairs to get the charger. The Surface Pro charger will charge the Surface RT as well, getting a full charge in well under two hours this way.
Trying this out shows the difference in the magnetic power port more clearly; the power connector that fits snugly and seamlessly into the Pro power port is just a fraction deeper than the port on the side of the Surface RT.
The combination of the longer connector and stronger magnets in the power port and the slightly different angle at the edge of the case make it easier to get the power connected every time - something that's just too fiddly on the Surface RT.
The magnet is also stronger on the keyboard connector - strong enough that you can attach the pen here, although not as neatly as in the power port. This doesn't just make it easier to snap the keyboard into place, it also means that new accessories using the extra power lines in the connector will attach firmly. We're hoping for a keyboard with an extra battery in, or a docking station.
As you'd expect from a Core i5 Ultrabook that just happens not to have a permanent keyboard, the Surface Pro is fast. It boots in about six seconds, and takes the same time to resume from hibernation once you add that to the power menu.
When running Photoshop and applying complex filters, editing 15GB raw images in Lightroom, rendering HD videos in Premiere Pro, watching 450 fish swimming at 60fps in the FishIE benchmark, the Core i5-3317U in the Surface Pro shows its speed and power.
You'll have no problem transcoding audio and video, running Visual Studio or using modelling and CAD software.
If you've used one of the very latest Core i5 processors, you know what sort of performance to expect from the Surface Pro. If you've used one of last year's Core i5 notebooks, the Surface Pro is definitely faster.
Of course, the Surface Pro is no Spring chicken anymore, which also means that, to its advantage, Microsoft has released several firmware updates to improve factors such as all round performance and battery life.
Microsoft's July 2014 Surface Pro July firmware update, for example, counted improved battery life management when a Surface cover is attached, improved Miracast wireless display functionality, enhanced compatibility for DisplayPort monitors, among others. For a full list of improvements baked into the update, click here.