Same here, iOS 10.2 actually made the problem worse.
The battery percentage seems to get stuck at some level for a while, even with battery draining apps such as pokemon go running, then it drops different percentages at different moments, it's really random.
For example, today I went out with nearly 90% battery, I open pokemon go and I know that drains the battery, so kind of quickly it went down to 80%, normal.
I was using a transit tracking app (of course uses GPS like pokemon go) and by the time I got on the bus, the battery dropped suddenly 10%. I used my phone very little then and then the battery dropped another 20% (it wasn't going down quickly, just dropped 20% at once), so I was at about 45%, I went home and it went down to 36%, plugged the phone and oh miracle... 76%.
It's not the battery, it would be if the phone went rapidly from let's say 20% to zero and it would always be the same, this is random, happens at any time with any percentage.
Apple support checked my battery and it's fine, they recommended me to set the phone as a new phone and to not restore from backup. I did set it as new but restored the backup, the idea that the data is causing problems is ridiculous and even if you restore from backup, all the apps are reinstalled from the iTunes library. I also know that many people tried that solution and it didn't work, so I am not ready to go through the pain of doing that for nothing.
I am 100% sure it's an iOS issue and I think it's related to GPS, either directly or because GPS consumes a lot of battery and somehow messes up the battery reading.
In any case, Apple needs to sort this out, this is getting silly now.