Battery monitory sees only battery 1. However, here is the output of upower:
$ upower -e
/org/freedesktop/UPower/devices/line_power_ADP1
/org/freedesktop/UPower/devices/battery_BAT1
/org/freedesktop/UPower/devices/battery_BAT2

$ upower -i /org/freedesktop/UPower/devices/battery_BAT1
  native-path:          BAT1
  vendor:               Sony Corporation
  power supply:         yes
  updated:              Fri 25 Oct 2013 10:57:59 PM CEST (132 seconds ago)
  has history:          yes
  has statistics:       yes
  battery
    present:             yes
    rechargeable:        yes
    state:               fully-charged
    energy:              45.49 Wh
    energy-empty:        0 Wh
    energy-full:         45.49 Wh
    energy-full-design:  51.06 Wh
    energy-rate:         0.049 W
    voltage:             12.423 V
    percentage:          100%
    capacity:            89.0913%
    technology:          lithium-ion

$ upower -i /org/freedesktop/UPower/devices/battery_BAT2
  native-path:          BAT2
  vendor:               Sony Corporation
  power supply:         yes
  updated:              Fri 25 Oct 2013 10:59:59 PM CEST (14 seconds ago)
  has history:          yes
  has statistics:       yes
  battery
    present:             yes
    rechargeable:        yes
    state:               charging
    energy:              50.29 Wh
    energy-empty:        0 Wh
    energy-full:         50.29 Wh
    energy-full-design:  51.06 Wh
    energy-rate:         5.001 W
    voltage:             12.442 V
    percentage:          100%
    capacity:            98.492%
    technology:          lithium-ion
  History (rate):
    1382734799  5.001   charging
    1382734769  5.162   charging
    1382734739  5.410   charging
    1382734709  5.745   charging

Obviously, two batteries are present and computer sees it.



Minor remark: the bug has been introduced roughly 1-1.5 years ago, don't remember when but it was working long time ago.

Reproducible: Always

Steps to Reproduce:
1. Plug in extension battery pack.
2. Run upower to cross-check.
3.
Actual Results:  
I saw that the battery monitor does not see my second battery.

Expected Results:  
Both batteries are visible.