If one uses gnome-power-manager on a laptop, one can see a history of the charge level of the battery and other things. But all that history is lost on reboot (which has an adverse effect on the accuracy statistics).

upowerd is actually what saves the history. It tries to save it in /var/lib/upower/, but that folder isn't created one way or the other when the archlinux upower package is installed. If one creates /var/lib/upower (root:root rwxr-xr-x), reboots, allows their battery to drain or charge for a few minutes, then reboots again, one can see that the statistics were saved in the folder in question, and are also visible in gnome-power-manager.

Basically, the upower package should somehow contain or create /var/lib/upower/.

tested with upower 0.9.1-1, gnome-power-manager 2.30.0-1