Wrong "time-to-empty" for multiple battery laptop

[Joschi Brauchle]

Hello everyone,

I have the following problem with a Lenovo Thinkpad T440s laptop, but is 
looks like a much more general problem that affects may users (will 
provide bugzilla links later):

The are two batteries installed in this machine:
mo-thinkpad01:~ # upower -i /org/freedesktop/UPower/devices/battery_BAT0
   native-path:          BAT0
   vendor:               SONY
   model:                45N1111
   serial:               12294
   power supply:         yes
   updated:              Fri 28 Feb 2014 09:37:25 AM CET (1202 seconds ago)
   has history:          yes
   has statistics:       yes
   battery
     present:             yes
     rechargeable:        yes
     state:               fully-charged
     energy:              23.2 Wh
     energy-empty:        0 Wh
     energy-full:         23.2 Wh
     energy-full-design:  23.2 Wh
     energy-rate:         0 W
     voltage:             12.471 V
     percentage:          100%
     capacity:            100%
     technology:          lithium-polymer

mo-thinkpad01:~ # upower -i /org/freedesktop/UPower/devices/battery_BAT1
   native-path:          BAT1
   vendor:               LGC
   model:                45N1127
   serial:               4696
   power supply:         yes
   updated:              Fri 28 Feb 2014 09:57:25 AM CET (3 seconds ago)
   has history:          yes
   has statistics:       yes
   battery
     present:             yes
     rechargeable:        yes
     state:               discharging
     energy:              22.94 Wh
     energy-empty:        0 Wh
     energy-full:         24.75 Wh
     energy-full-design:  23.48 Wh
     energy-rate:         2.239 W
     voltage:             12.51 V
     time to empty:       10.2 hours
     percentage:          92%
     capacity:            100%
     technology:          lithium-ion
   History (rate):
     1393577845  2.239   discharging
     1393577815  1.652   discharging
     1393577785  1.690   discharging
     1393577755  1.803   discharging


As you can see, only BAT1 is being discharged, whereas BAT0 stays fully 
charged.

Thus, the "time-to-empty" flag is only available for BAT1 and clearly 
only displays the time to empty FOR THAT PARTICULAR battery, but not 
when using ALL batteries.

As a result, the current "time-to-empty" is basically a useless 
information for the user, as it ignores the second, fully charged and 
available battery.

Imagine the case where BAT1 = 5% charged and discharging and BAT0 = 100% 
fully-charged. Then upower will display something like ~5 minutes 
remaining battery life (because it ignores BAT0), but in reality the 
total lifetime of BAT0+BAT1 would be multiple hours.

Is this a known limitation?

I would like upower to provide an additional "overall-time-to-empty" 
value using ALL batteries / energy sources installed.

Best regards,
Joschi Brauchle
-- 
Dipl.-Ing. Joschi Brauchle, M.S.

Institute for Communications Engineering (LNT)
Technische Universitaet Muenchen (TUM)
80290 Munich, Germany

Tel (work): +49 89 289-23474
Fax (work): +49 89 289-23490
E-mail: joschi.brauchle at tum.de
Web: http://www.lnt.ei.tum.de/

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