Comment 3 for bug 64752

Interesting data from lshal:

BAT1:
  battery.remaining_time = 1031 (0x407) (int)
  battery.charge_level.percentage = 100 (0x64) (int)
  battery.charge_level.rate = 5162 (0x142a) (int)
  battery.charge_level.last_full = 1479 (0x5c7) (int)
  battery.charge_level.current = 1479 (0x5c7) (int)
  battery.rechargeable.is_discharging = true (bool)
  battery.rechargeable.is_charging = false (bool)

BAT2:
  battery.remaining_time = 7627 (0x1dcb) (int)
  battery.charge_level.percentage = 100 (0x64) (int)
  battery.charge_level.rate = 5189 (0x1445) (int)
  battery.charge_level.last_full = 10994 (0x2af2) (int)
  battery.charge_level.current = 10994 (0x2af2) (int)
  battery.rechargeable.is_discharging = true (bool)
  battery.rechargeable.is_charging = false (bool)

As you can see, both batteries are fully charged and both are discharging (this is different than on my HP nw8240 where external battery is discharged first). You may also notice that two batteries have very different capacity (1479 vs. 10994) which impacts very different remaining time (1031 vs. 7627).
It is very likely that first battery is old and therefore cannot provide full capacity anymore. This is why you may get less juice out than you would anticipate.

On the other hand, you can now configure in power-manager when the laptop critical action should be performed - the default is 5 min and this may be too high for your laptop (I have it on 0 min as this is still enough juice to properly hibernate my laptop)