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.
Here you can see the battery capacity history from
powercfg /batteryreport. How suspiciously convenient that the degradation starts occurring close to the 1-year mark, when most owners are going to be out of warranty...
|PERIOD||FULL CHARGE CAPACITY||DESIGN CAPACITY|
|2015-11-15 - 2015-11-23||41,239 mWh||42,157 mWh|
|2015-11-23 - 2015-11-29||41,105 mWh||42,157 mWh|
|2015-11-29 - 2015-12-06||40,587 mWh||42,157 mWh|
|2015-12-06 - 2015-12-13||40,885 mWh||42,157 mWh|
|2015-12-13 - 2015-12-21||40,838 mWh||42,157 mWh|
|2015-12-21 - 2015-12-29||40,876 mWh||42,157 mWh|
|2015-12-29 - 2016-01-03||40,576 mWh||42,157 mWh|
|2016-01-03 - 2016-01-11||40,824 mWh||42,157 mWh|
|2016-01-11 - 2016-01-18||41,131 mWh||42,157 mWh|
|2016-01-18 - 2016-01-25||41,299 mWh||42,157 mWh|
|2016-01-25 - 2016-02-07||41,268 mWh||42,157 mWh|
|2016-02-07 - 2016-02-14||41,201 mWh||42,157 mWh|
|2016-02-14 - 2016-02-22||41,683 mWh||42,157 mWh|
|2016-02-22 - 2016-03-06||41,256 mWh||42,157 mWh|
|2016-03-06 - 2016-03-14||41,070 mWh||42,157 mWh|
|2016-03-14 - 2016-03-21||40,945 mWh||42,157 mWh|
|2016-03-21 - 2016-03-28||40,494 mWh||42,157 mWh|
|2016-03-28 - 2016-04-04||40,061 mWh||42,157 mWh|
|2016-04-04 - 2016-04-13||38,910 mWh||42,157 mWh|
|2016-04-13 - 2016-04-18||38,258 mWh||42,157 mWh|
|2016-04-18 - 2016-04-25||38,197 mWh||42,157 mWh|
|2016-04-25 - 2016-05-01||38,349 mWh||42,157 mWh|
|2016-05-01 - 2016-05-09||37,741 mWh||42,157 mWh|
|2016-05-09 - 2016-05-15||38,124 mWh||42,157 mWh|
|2016-05-15 - 2016-05-22||38,173 mWh||42,157 mWh|
|2016-05-22 - 2016-05-29||39,119 mWh||42,157 mWh|
|2016-05-29 - 2016-06-05||41,869 mWh||42,157 mWh|
|2016-06-05 - 2016-06-12||42,583 mWh||42,157 mWh|
|2016-06-12 - 2016-06-19||39,968 mWh||42,157 mWh|
|2016-06-19 - 2016-06-26||33,398 mWh||42,157 mWh|
|2016-06-26 - 2016-07-03||32,490 mWh||42,157 mWh|
|2016-07-03 - 2016-07-10||26,051 mWh||42,157 mWh|
|2016-07-11||23,682 mWh||42,157 mWh|
|2016-07-12||23,682 mWh||42,157 mWh|
|2016-07-13||21,530 mWh||42,157 mWh|
|2016-07-14||18,453 mWh||42,157 mWh|
|2016-07-15||18,453 mWh||42,157 mWh|
|2016-07-16||18,453 mWh||42,157 mWh|
|2016-07-17||18,453 mWh||42,157 mWh|
|2016-07-18||18,453 mWh||42,157 mWh|
|2016-07-19||18,453 mWh||42,157 mWh|
|2016-07-20||18,453 mWh||42,157 mWh|
|2016-07-21||18,453 mWh||42,157 mWh|
|2016-07-22||18,453 mWh||42,157 mWh|