laptop_battery_monitor: breaks when discharging

[kdhansen]

I am running Ubuntu Xenial 16.04 with Kinetic in a VirtualBox on a MacBook Pro, so I don't know if this is a general problem to Xenial/Kinetic or some artifact of the VirtualBox.

The laptop_battery_monitor works while the laptop is plugged in to the mains, but when the adapter is disconnected, the node dies. Resulting in:

[WARN] [WallTime: 1472477308.423277] Battery : unable to check laptop battery state [[Errno 19] No such device]
[laptop_battery-2] process has finished cleanly

I tracked it down to what I think is a kernel module problem. Running grep "" * in /sys/class/power_supply/BAT0/ when plugged in gives:

alarm:0
capacity:100
capacity_level:Full
cycle_count:0
grep: device: Is a directory
energy_full:50000000
energy_full_design:50000000
energy_now:50000000
manufacturer:innotek
model_name:1
grep: power: Is a directory
power_now:0
present:1
serial_number:0
status:Full
grep: subsystem: Is a directory
technology:Unknown
type:Battery
uevent:POWER_SUPPLY_NAME=BAT0
uevent:POWER_SUPPLY_STATUS=Full
uevent:POWER_SUPPLY_PRESENT=1
uevent:POWER_SUPPLY_TECHNOLOGY=Unknown
uevent:POWER_SUPPLY_CYCLE_COUNT=0
uevent:POWER_SUPPLY_VOLTAGE_MIN_DESIGN=10000000
uevent:POWER_SUPPLY_VOLTAGE_NOW=10000000
uevent:POWER_SUPPLY_POWER_NOW=0
uevent:POWER_SUPPLY_ENERGY_FULL_DESIGN=50000000
uevent:POWER_SUPPLY_ENERGY_FULL=50000000
uevent:POWER_SUPPLY_ENERGY_NOW=50000000
uevent:POWER_SUPPLY_CAPACITY=100
uevent:POWER_SUPPLY_CAPACITY_LEVEL=Full
uevent:POWER_SUPPLY_MODEL_NAME=1
uevent:POWER_SUPPLY_MANUFACTURER=innotek
uevent:POWER_SUPPLY_SERIAL_NUMBER=0
voltage_min_design:10000000
voltage_now:10000000

Whereas when the power is unplugged we get:

alarm:0
capacity:100
capacity_level:Normal
cycle_count:0
grep: device: Is a directory
energy_full:50000000
energy_full_design:50000000
energy_now:50000000
manufacturer:innotek
model_name:1
grep: power: Is a directory
grep: power_now: No such device
present:1
serial_number:0
status:Discharging
grep: subsystem: Is a directory
technology:Unknown
type:Battery
uevent:POWER_SUPPLY_NAME=BAT0
uevent:POWER_SUPPLY_STATUS=Discharging
uevent:POWER_SUPPLY_PRESENT=1
uevent:POWER_SUPPLY_TECHNOLOGY=Unknown
uevent:POWER_SUPPLY_CYCLE_COUNT=0
uevent:POWER_SUPPLY_VOLTAGE_MIN_DESIGN=10000000
uevent:POWER_SUPPLY_VOLTAGE_NOW=10000000
uevent:POWER_SUPPLY_ENERGY_FULL_DESIGN=50000000
uevent:POWER_SUPPLY_ENERGY_FULL=50000000
uevent:POWER_SUPPLY_ENERGY_NOW=50000000
uevent:POWER_SUPPLY_CAPACITY=100
uevent:POWER_SUPPLY_CAPACITY_LEVEL=Normal
uevent:POWER_SUPPLY_MODEL_NAME=1
uevent:POWER_SUPPLY_MANUFACTURER=innotek
uevent:POWER_SUPPLY_SERIAL_NUMBER=0
voltage_min_design:10000000
voltage_now:10000000

As you can see power_now is present but there is no device.

A fix may be to change line 181 and 182 to

try:
    rv.current = _read_number(_battery_acpi_path + '/power_now')/10e5 / \
        _read_number(_battery_acpi_path + '/voltage_now')
    except IOError:
        rv.current = 0

But then the node would report 0 even though the current may be something else.