For mobile users it is crucial to know remaining battery time. I submitted two small console tools for 2.x which may help.
acpiThis is displaying information provided by BIOS (if supported). Starting as 'acpi -V' all information displayed. On my Acer notebook it looks like:
Battery 0: Discharging, 86%, 01:47:31 remaining
Battery 0: design capacity 4000 mAh, last full capacity 3759 mAh = 93%
Adapter 0: off-line
Thermal 0: ok, 50.0 degrees C
Thermal 0: trip point 0 switches to mode critical at temperature 100.0 degrees C
Cooling 0: Processor 0 of 10
Cooling 1: Processor 0 of 10
It also indicates charging, but on my machine no remaining charging time displayed.
As usual, displayed remaining time is usually longer than the reale time experienced, but it is up to the ACPI BIOS.
ibamThe Intelligent BAttery Monitor is a more advanced tool. It measures charging and discharging characteristics and stores measurements in home directory. Displayed time is calculated not only info provided by BIOS but its own measurements, therefore more accurate and if you are using frequently learns the machine.
Read docs at
http://ibam.sourceforge.net/ for more info.
To get accurate figures save measurement data. If taking full discharging characteristrics don't forget to save manually home directory just before battery is full out otherwise data will be lost.