When battery fails to report charge:
$ cat /sys/class/power_supply/BAT0/present
1
$ cat /sys/class/power_supply/BAT0/power_now
cat: /sys/class/power_supply/BAT0/power_now: No such device
$ cat /sys/class/power_supply/BAT0/voltage_now
cat: /sys/class/power_supply/BAT0/voltage_now: No such device
$ cat /sys/class/power_supply/BAT0/energy_full
66390000
$ cat /sys/class/power_supply/BAT0/energy_now
cat: /sys/class/power_supply/BAT0/energy_now: No such device
While this is going on, I can normally use the laptop on battery - it just does
not report the charge level at all.
Sometimes the battery will report its charge level correctly:
$ cat /sys/class/power_supply/BAT0/capacity
86
$ cat /sys/class/power_supply/BAT0/power_now
21977000
$ cat /sys/class/power_supply/BAT0/voltage_now
15598000
$ cat /sys/class/power_supply/BAT0/energy_now
56910000
Sometimes the battery will go from reporting charge correctly to not reporting
charge level while the laptop is on battery power. I have not figured out any
way to reproduce either condition reliably.