Update 3 July 26, 2016: The techs were able to confirm the issue and offered me a same-device refurb replacement. The replacement is a newer-revision SP3 with an LGC-LGC battery

and came with Windows 10 build 1511 pre-installed. I'm a happy camper. Thanks for (finally) doing the right thing, Microsoft.

Update 2 July 25, 2016: Came back to the Microsoft Store after they told me they didn't find anything wrong after charging it and leaving it unplugged for 6 hours. Yeah, well, it might help to disable sleep mode if you're going to perform a battery rundown test (facepalm!) And apparently, powercfg is a new thing for the monkeys at the Microsoft Store. Anyhow, after showing the tech all that and also making him witness my Surface losing 10% of its battery in about as many minutes, he finally agreed that something was wrong. Long story short, the last thing they want to do before replacing my device is a wipe and factory reset to rule out any software cause. (To me it's more likely that Microsoft themselves pushed out a bad firmware update with faulty power management...) Fingers crossed...

Update 1 July 23, 2016: Brought my Surface to the local Microsoft store. My device is technically a few days out of warranty but they were willing to work with me. I handed it over to them so they could "run diagnostics". Told to check back in 1-3 days. There's the possibility I'll be able to exchange my Surface if the diagnostic comes back faulty.

After seeing articles like this in my news feed, I ran powercfg /batteryreport on my Surface Pro 3 to check if I might be affected. Unfortunately, the answer is yes, to say the least...

To be honest I haven't really been noticing as my Surface has mostly been sitting at home connected to an AC adapter, but when school starts up this is going to be a major pain in the ass. I'm typing this while on battery and I can see the battery life percentage decreasing almost in real time. In less than half an hour it's gone down from 100% to 67%.

I'm debating whether or not a trip to the local Microsoft Store is worth it. Surface phone support seems to be useless - if you're no longer under warranty they want $450 from you to do a replacement. I wonder if the support techs simply aren't aware of this being a widespread issue, or if Microsoft just doesn't care...either way, there's probably going to be a lot of pissed-off SP3 users soon.