Open Radar

 
Summary:
Currently in iOS, the 20% and 10% battery warning notifications only appear (as modal alerts) when the iPhone is unlocked/awake, e.g. if my phone drops below 10% charge while it is locked/asleep and I am not using it, I will only receive the low battery warning when I unlock the phone, learning via modal alert that the battery has 10% remaining when perhaps the remaining value in the status bar is already reading 8%.

Recently, my phone ended up dying on me without my knowledge; I had last checked it sometime after 3 PM and the battery level was somewhere just under 20%, typically enough battery to last until I got home.  My first indication that something was wrong was that I saw that it was after 5:45 PM and I realized that my 5:45 reminder to start packing up in order to get home on time had not fired.  My phone was unresponsive and even after 15 minutes of charging, it would not turn on.  

At about 7:30 PM, after having been charging for more than an hour and executing a "hard reboot" sequence, the phone finally powered on to the "needs more charging before it can boot" screen, and about 15 minutes later, the phone booted with a 1% charge (and a notification generated by my broker at 3:55 PM that showed up as having just arrived).  I also learned I had missed important calls and texts about the alarm system at the office.  

All in all, I had no access to my phone or any of its computer-like functions for roughly 4 hours, which could have been easily avoided (baring the problem having been some sort of catastrophic battery drain) by an audible notification that my phone was in a low battery state while it was locked.  Upon hearing that notification, I would have realized that the battery was draining faster than usual that afternoon and would have put the phone on the charger, rather than being blissfully ignorant of the fact my primary communication method was non-functional for several hours and would continue to be non-functional for several more hours.

Steps to Reproduce:
1. Use iPhone until it is below 20% charge and close to, but above, 10% charge.
2. Put iPhone to sleep with the lock/sleep button.
3. Carry iPhone around while walking, or leave it on a desk in an area with intermittent low signal, i.e., situations that will cause iPhone to continue to passively use battery and eventually drop below 10% charge.


Expected Results:
4. iPhone fires notification message on lock screen, accompanied by sound, that alerts me to the fact the battery charge has dropped to 10% while phone was sleeping/locked.

Actual Results:
4. Have a need to perform some activity that requires waking/unlocking iPhone.
5. Receive 10% Battery warning modal alert *after* unlocking.
6. Optional: Observe that battery level in status bar may already be below 10%

Version:
iOS 8.3 (12F70)

Notes:
The 20% Battery notification may also benefit from being sent when the phone is asleep/locked, but the 10% Battery notification is the more important one, since it is the last alert anyone might receive before the phone must power down.

Configuration:
iPhone 5s, 16GB, Verizon, using both Wi-Fi and Cellular