Hello, I'm running kernel 3.0.0 from Debian testing. On my new Thinkpad X220, I noticed that the "acpi" command gives way too optimistic "remaining time on battery" estimates. To calculate the remaining time, the "acpi" tools divides the "charge_now" value by "current_now" which seems to make sense physically if the units of these values would be what the names imply. However, this gives a remaining time of 5.35 hours which is way too high for the small 4 cell battery I have. Let's look at a snapshot of the BAT0 directory: /sys/class/power_supply/BAT0% grep . * alarm:156000 charge_full:3135000 charge_full_design:2886000 charge_now:2761000 current_now:516000 cycle_count:0 manufacturer:SANYO model_name:42T4899 present:1 serial_number:19797 status:Discharging technology:Li-ion type:Battery uevent:POWER_SUPPLY_NAME=BAT0 uevent:POWER_SUPPLY_STATUS=Discharging uevent:POWER_SUPPLY_PRESENT=1 uevent:POWER_SUPPLY_TECHNOLOGY=Li-ion uevent:POWER_SUPPLY_CYCLE_COUNT=0 uevent:POWER_SUPPLY_VOLTAGE_MIN_DESIGN=14800000 uevent:POWER_SUPPLY_VOLTAGE_NOW=15993000 uevent:POWER_SUPPLY_CURRENT_NOW=516000 uevent:POWER_SUPPLY_CHARGE_FULL_DESIGN=2886000 uevent:POWER_SUPPLY_CHARGE_FULL=3135000 uevent:POWER_SUPPLY_CHARGE_NOW=2761000 uevent:POWER_SUPPLY_MODEL_NAME=42T4899 uevent:POWER_SUPPLY_MANUFACTURER=SANYO uevent:POWER_SUPPLY_SERIAL_NUMBER=19797 voltage_min_design:14800000 voltage_now:15993000 The nominal energy capacity of my battery is 29 Wh, so charge_now seems to be in units of 10 µWh! (Yes, charge_now == 2761000 seems to mean that the _energy_ is 27.61 Wh.) This is bogus! current_now and voltage_now seem to be in the reasonable units µA and µV, as current_now * voltage_now * 1e-12 = 8.25 which seems to be the correct power in Watts. (This is also the power which "powertop" is reporting.) The remaining runtime in hours in my case seems to be given by charge_now * 1e-5 / (current_now * voltage_now * 1e-12) = 3.35 which looks like a good estimate of the real situation. This does not seem to be the way things are supposed to be. The kernel source file include/linux/power_supply.h states /* * All voltages, currents, charges, energies, time and temperatures in uV, * µA, µAh, µWh, seconds and tenths of degree Celsius unless otherwise * stated. It's driver's job to convert its raw values to units in which * this class operates. */ So this seems to be a bug of either the battery driver or the internal battery software. I hope this report will be useful for linux ACPI developers. Christoph -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
