Interpreting LowBatteryLog

First off, find the file

Go to:
Settings > Privacy & Security > Analytics & Improvements > Analytics Data
Then scroll until you find a file named [LowBatteryLog-YYYY-MM-DD]

Therein you should find a snippet similar to this
Foreground Applications: com.google.maps
Screen Brightness: 0.534646
Hardware Model: D49AP
Awake Time: 02:41:19 (9679)
Standby Time: 11:26:34 (41194)
Partial Charge: 0
Capacity: 0
Voltage: 3647 mV
I will now explain what each line mean

Foreground Applications: tells you what app it had open. in this case it was google maps
This line will only exist if the display was on, in an app while it ran out of power.

Screen Brightness: this is the screen brightness, it has value between 0.0(0%) and 1.0 (100%)
This will only show if the display was on while it ran out of power

This Line tells us the model, but we would already know that, so it does not matter.

Awake Time: 02:41:19 (9679)
Standby Time: 11:26:34 (41194)
Standby time is actually "Time since full charge"
Awake time is the amount of that time the Display was on. meaning it can NEVER be higher than standby time.

This suggests that the user either used the phone heavily or that the battery needs replacement... maybe both.

Partial Charge: 0 Tells us that the phone had not been "trickle charging"
This value is either 0 or 1.
1 = have been plugged in since last full charge
0 = Have not been plugged in since last full charge

Capacity: 0 this is the battery percentage of the phone when it turned off.
if it is over 1 you should probably replace the battery.

This is the recorded voltage of the battery. it should be close to the expected value when it is on.

Understand IOS LowBatteryLog