Linux – Understanding battery information

linuxpower-management

My laptop is Lenovo T400 and OS is Ubuntu 10.10. Here is information about my battery:

$ cat /proc/acpi/battery/BAT0/state 
present:                 yes
capacity state:          ok
charging state:          charged
present rate:            0 mW
remaining capacity:      28730 mWh
present voltage:         11390 mV

$ cat /proc/acpi/battery/BAT0/info
present:                 yes
design capacity:         56160 mWh
last full capacity:      58730 mWh
battery technology:      rechargeable
design voltage:          10800 mV
design capacity warning: 2936 mWh
design capacity low:     200 mWh
cycle count:          0
capacity granularity 1:  1 mWh
capacity granularity 2:  1 mWh
model number:            42T4653
serial number:             285
battery type:            LION
OEM info:                LGC

$ cat /proc/acpi/battery/BAT0/alarm
alarm:                   2936 mWh
  1. I was wondering if 1-(remaining capacity/design capacity) is the
    current charged percentage of the battery?
  2. Since present rate is 0 mW, does it mean that the battery is
    currently not charging nor discharging?
  3. Is the present voltage (11390 mV) being bigger than the design voltage (10800 mV) a bad
    thing? If yes, what can I do about it? My laptop is currently using
    power from power cord.

Thanks and regards!

Best Answer

    1. Yes and no - it depends on the tool that would calculate the percentage. Probably the more common interpretation is 1-(remaining capacity/last full capacity) - this is because the last full capacity indicates how far the battery can be currently charged and that number decreases as the your battery wears out.

    2. Yes - this is also indicated by charging state: charged in the state information.

    3. The higher voltage is nothing to worry about - this must be so because it is how batteries work. If you measure the voltage on a popular AA battery (that "by design" should be 1.5V), you'll see the voltage can be higher or lower than the "design", depending on how much energy is there left. That is the physical nature of batteries.