Estimated read time: 1 minutes
Probably most mobile users know the 'acpi' command, a simple command-line utility that shows the state of the battery on a PC.
The problem is that iBooks have PMU, not ACPI support, so that problem can hardly output anything useful. I searched for an equivalent for a while, but actually couldn't find such a utility, and quite frankly, it's not a big deal to write such a one, so I stopped wasting with searching alternatives, I just wrote one.
$ acpi Battery 1: discharging, 92%, 04:34:17 remaining
$ acpi Battery 1: charging, 99%, 00:10:53 until charged
$ acpi Battery 1: charged, 100%
The short script (54 lines) is available here.