Re: incorrect battery reading, 0% all the time

Jun 3, 2026 3:52:35 AM Jan Stary <[email protected]>:

>> On my Dynabook Portege X40-J running OpenBSD 7.9, the battery report
>> from `apm -v` always returns 0% despite the battery being fully
>> charged and AC connected.
>> AC/BAT state does change when AC is connected/disconnected, only the
>> battery remains at 0%.
>>
>> apm -v output
>> (AC UNPLUGGED)
>> Battery state: charging, 0% remaining, 0 minutes recharge time 
>> estimate
>> AC adapter state: connected
>> Performance adjustment mode: manual (2901 MHz)
>> (AC PLUGGED)
>> Battery state: CRITICAL, 0% remaining, 0 minutes life estimate
>> AC adapter state: not connected
>> Performance adjustment mode: auto (400 MHz)
>>
>> There's nothing wrong with the battery physically, it reports
>> correctly under Linux and holds charge well.
>
> So what does it report under Linux?
> (And other OSes, for that matter?)
>
>> Attached is dmesg and sysctl output
>
> sysctl hw would probably be enough for this :-)
>
>> acpibat0 at acpi0: BAT1 model "G71C000MA210" serial 4266600 type LiON 
>> oem "BYD"
>
>> hw.sensors.acpibat0.volt0=4266.60 VDC (voltage)
>> hw.sensors.acpibat0.volt1=4266.60 VDC (current voltage)
>> hw.sensors.acpibat0.power0=1804.16 W (rate)
>
> Batteries differ in the semantics of what they report
> - surely it's not 4 kV and 1.8kW; probably mili.
>
>> hw.sensors.acpibat0.watthour0=1804.16 Wh (last full capacity)
>
> It seems odd that this is exactly the same number
> as the rate above in (mili)watts.
>
>> hw.sensors.acpibat0.watthour1=3300.26 Wh (warning capacity)
>> hw.sensors.acpibat0.watthour2=0.00 Wh (low capacity)
>> hw.sensors.acpibat0.watthour3=3308.11 Wh (remaining capacity), WARNING
>> hw.sensors.acpibat0.watthour4=1804.16 Wh (design capacity)
>
> So 3308 Wh of the designed 1804 Wh remain?
>
> I suspect the battery itself reporting something strange
> - possibly linux's acpibat knows its quirks?
>
>     Jan

Thanks for your time, below is the information pulled from Void Linux and 
FreeBSD (Live USB) while AC is unplugged.

Void Linux: upower (3rd party program), print contents of files under 
/sys/class/power_supply/BAT1
FreeBSD: acpiconf, sysctl


--------------------------
Void Linux (Kernel 7.0.11)
--------------------------
$ upower dump
Device: /org/freedesktop/UPower/devices/battery_BAT1
  native-path:          BAT1
  vendor:               BYD
  model:                G71C000MA210
  serial:               263
  power supply:         yes
  updated:              Wed Jun  3 04:57:13 2026 (0 seconds ago)
  has history:          yes
  has statistics:       yes
  battery
    present:             yes
    rechargeable:        yes
    state:               discharging
    warning-level:       none
    energy:              22.576 Wh
    energy-empty:        0 Wh
    energy-full:         27.612 Wh
    energy-full-design:  53.13 Wh
    energy-rate:         6.175 W
    voltage:             15.4 V
    charge-cycles:       N/A
    time to empty:       3.7 hours
    percentage:          82%
    capacity:            51.9706%
    technology:          lithium-ion
    icon-name:          'battery-full-symbolic'
  History (rate):
    1780477033    6.175    unknown
    1780477032    5.990    discharging
    1780477030    5.467    discharging
    1780477029    5.128    discharging
    1780477027    6.160    discharging
    1780477025    6.190    discharging
    1780477024    5.436    discharging
    1780477022    6.391    discharging
    1780476965    5.846    discharging
----trimmed

$ find /sys/class/power_supply/BAT1/ -type f | xargs grep .
/sys/class/power_supply/BAT1/uevent:DEVTYPE=power_supply
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_NAME=BAT1
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_TYPE=Battery
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_STATUS=Discharging
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_PRESENT=1
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_TECHNOLOGY=Li-ion
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_CYCLE_COUNT=0
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_VOLTAGE_MIN_DESIGN=15400000
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_VOLTAGE_NOW=15400000
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_POWER_NOW=12859000
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_ENERGY_FULL_DESIGN=53130000
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_ENERGY_FULL=27612000
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_ENERGY_NOW=20589000
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_CAPACITY=75
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_CAPACITY_LEVEL=Normal
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_TYPE=Battery
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_MODEL_NAME=G71C000MA210
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_MANUFACTURER=BYD
/sys/class/power_supply/BAT1/uevent:POWER_SUPPLY_SERIAL_NUMBER=263
/sys/class/power_supply/BAT1/serial_number:263
/sys/class/power_supply/BAT1/technology:Li-ion
/sys/class/power_supply/BAT1/power_now:12859000
/sys/class/power_supply/BAT1/present:1
/sys/class/power_supply/BAT1/power/runtime_active_time:0
/sys/class/power_supply/BAT1/power/runtime_status:unsupported
/sys/class/power_supply/BAT1/power/runtime_suspended_time:0
/sys/class/power_supply/BAT1/power/control:auto
/sys/class/power_supply/BAT1/manufacturer:BYD
/sys/class/power_supply/BAT1/energy_now:20589000
/sys/class/power_supply/BAT1/type:Battery
/sys/class/power_supply/BAT1/capacity:75
/sys/class/power_supply/BAT1/cycle_count:0
/sys/class/power_supply/BAT1/voltage_now:15400000
/sys/class/power_supply/BAT1/status:Discharging
/sys/class/power_supply/BAT1/alarm:0
/sys/class/power_supply/BAT1/model_name:G71C000MA210
/sys/class/power_supply/BAT1/voltage_min_design:15400000
/sys/class/power_supply/BAT1/hwmon3/in0_input:15400
/sys/class/power_supply/BAT1/hwmon3/power/runtime_active_time:0
/sys/class/power_supply/BAT1/hwmon3/power/runtime_status:unsupported
/sys/class/power_supply/BAT1/hwmon3/power/runtime_suspended_time:0
/sys/class/power_supply/BAT1/hwmon3/power/control:auto
/sys/class/power_supply/BAT1/hwmon3/power1_input:12859000
/sys/class/power_supply/BAT1/hwmon3/name:BAT1
/sys/class/power_supply/BAT1/capacity_level:Normal
/sys/class/power_supply/BAT1/energy_full_design:53130000
/sys/class/power_supply/BAT1/charge_control_end_threshold:100
/sys/class/power_supply/BAT1/energy_full:27612000

--------------------
FreeBSD 15.0-RELEASE
--------------------
# acpiconf -i 0
Design capacity:             53130 mWh
Last full capacity:          27612 mWh
Technology:                  primary (non-rechargeable)
Design voltage:              15400 mV
Capacity (warn):             552 mWh
Capacity (low):              0 mWh
Low/warn granularity:        531 mWh
Warn/full granularity:       531 mWh
Model number:                G71C000MA210
Serial number:               263
Type:                        LiON
OEM info:                    BYD
State:                       discharging
Remaining capacity:          65%
Remaining time:              1:37
Present rate:                11041 mW
Present voltage:             15400 mV

# sysctl -a | grep -i battery
battery0: <ACPI Control Method Battery> on acpi0
hw.acpi.battery.info_expire: 5
hw.acpi.battery.units: 1
hw.acpi.battery.state: 1
hw.acpi.battery.rate: 10256
hw.acpi.battery.time: 99
hw.acpi.battery.life: 61
dev.battery.0.%iommu:
dev.battery.0.%parent: acpi0
dev.battery.0.%pnpinfo: _HID=PNP0C0A _UID=1 _CID=none
dev.battery.0.%location: handle=\_SB_.BAT1
dev.battery.0.%driver: battery
dev.battery.0.%desc: ACPI Control Method Battery
dev.battery.0.%parent: