In scouring Josh Hickman's Android 12 test image, I came across a new folder that was previously found in previous test images. I can be found at the following path:
data\system\shutdown-checkpoints
Inside contains some plaintext files with a consistent naming convention. They can been seen titled checkpoints-<UNIX_timestamp>. Converting the UNIX timestamps it appears to match the last modified date of the files themselves.
Figure 1: checkpoints files
Figure 2: checkpoints-1638954568308 file contents
We can see 3 SYSTEM shutdown requests all around the same time 2021-12-08 at 4:09am, even one that gives a reason, the battery was dead. We see a hint from Josh's documentation that the phone was dead a few hours after that when he plugged it in:
Figure 3: Power Events from documentation
Opening the other sample file "checkpoints-1635255560545" we can see more shutdown events:
Figure 4: checkpoints-1635255560545 file contents
From Josh's documentation again, we can see a reboot was performed at the same time the file indicates, 2021-10-26 at 9:39am.
Figure 5: Power Events from documentation
Figure 6: Shutdown Checkpoints report in ALEAPP