@lakotaubp I let the phone fully discharge thrice, recharging until it becomes white. I checked this battery loss for few days. Then I moved N5 to stock Android, just to check how the battery works in it. Its 11.25 now, and N5 with stock Android had lost only 9%, while with UT, I had to start recharging at this time; it rapidly went down. Wifi on, LTE off, no phone calls, no smses whatever, just idling. I am going to check this for next few days with Android.
Btw, this should be in General, rather than Support. There is nothing much we can do to support old hardware. This N5 is made in May 2014, used by one person quite carefully. It took me quite while to find a decent one.
If the battery works quite well in Android, but poorly in UT, we have a problem, not with the hardware. The stock Android is using 3.4 kernel from September 2016. I think UT is using 4.4 kernel.