Update 9.2.1 is killing the battery, is an update coming?

I've had my iPhone 5S since it came out and never had any problems with it at all.

When not used, the phone would last almost 2 full days without recharge. When used, I would easily last 12 hours and more with heavy use unless Facebook's messenger was used, then more around 5-6 hours.

3 days ago I updated to iOS 9.2.1.

Now my phone dies within 4 hours, whether I use it or not. All notifications are off, bluetooth and wifi are off, no apps are running, not used at all, left alone on a table overnight. (My iPad Mini has the exact same problem since updating iOS 2 weeks ago.)

I've noticed the phone overheats constantly unless you turn it off completely, which is just insane and probably why the phone is dying. It's not a hardware issue, it's an update issue that's having an impact on the hardware and I'd like to know if there is a planned update to fix this issue.