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 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%)

Much like foreground applications this will only show if the display was on

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)

These line tells us for how long the phone was on since last full charge
so in this case it was on for (awake + standby)= 14 hours, 07 minutes, 53 Seconds

but the display was on for 2 hours and 41 minutes
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