I guess this will finish this off.
After the last battery drain instance, I shut the Forma down and restarted it. I charged it to 100% and put it to sleep at the home menu. Here's the battery use until the battery drained again:
- Charge to 100%
- Sleep, 12 hrs: 100% to 98% = 2%
- Read, 11:45 (98%) to 12:45 (87%) = 1 hour, 11%
- Sleep, 2 hrs: 87% to 86% = 1%
- Read, 2:45 (86%) to 3:45 (75%) = 1 hour, 11%
- Sleep, 2 hrs: 75% to 75% = 0%
- Read, 5:45 (75%) to 6:45 (62%) = 1 hour, 13%
- Sleep, 2 hrs: 62% to 50% = 12%
- Read, 8:45 (50%) to 9:45 (41%) = 1 hour, 9%
- Sleep, 10 hrs: 41% to 40% = 1%
- Read, 7:55 (41%) to 8:55 (27%) = 1 hour, 13%
- Sleep, 2-1/4 hrs: 27% to 27% = 0%
- Read, 11:10 (27%) to 12:01 (12:00 10% Warning, then Shut down 1 minute later. Plugged in, came up at 6%.)
In general, except for that last reading gasp of something between 27% and 21% in 50 minutes, the Forma used about 11% of battery per hour. A year ago, it was using about 8% an hour. But, that's acceptable. While sleeping, except for one case, the battery use was negligible (0% to 2%, regardless of time).
The problem is with that one 12% drain while asleep for 1 hour and the final loss of battery to the point of shutdown while reading. Plus, the 10% warning popping up one minute before the Forma actually shut down and wouldn't start up without being plugged in.
All of the above is with a freshly factory-reset Forma with all communications turned off and with no connections to a computer. So, at this point, there doesn't seem to be anything I can do except replace the thing. Pretty irritating for a 1-1/2 year old device.