Librem 13 battery power stats random

I have seen other discussions about battery power (notably here), but my issue seems somewhat different.

I am using a Librem 13 rev 3 with all Byzantium updates on Gnome.

A couple of months or so ago, I noticed the max time I had on the battery shrunk dramatically, from about 4 hrs 30 min to 2 hrs 30 mins. My Librem 13 is about 3 years old and I assumed that the battery was slowly dying, but the times and percentages seemed to be odd.

I sometimes find the time and percentage are totally random. For example, when I started work this morning, I had 2 hrs 33 min at about 90%. For the last 15 minutes–after an hour and 10 minutes–it has jumped to 100% at 4 hrs 38 minutes. It did this yesterday too after charging, while off, much of the day.

‘upower’ shows the battery staying at 100% too:

state:               discharging
energy:              29.7036 Wh
energy-full:         33.0632 Wh
energy-rate:         6.29 W
time to empty:       4.7 hours
percentage:          100%

While the energy and energy-full are certainly different, the percentage does not budge.

I am curious of others have seen this issue, or if there was a software update that introduced this behavior. The time and percentage have become (or always was?) more inaccurate than I would expect. Even as a ballpark, they are useless to me now. (Still at 100%)