Implement it on the Kobo Sage, for the PowerCover
TouchMenu: Display auxiliary battery status
Kobo: More accurately report the PowerCover's charging status
i.e., try to actually figure out if the auxiliary battery is charging
instead of just checking the reader's battery (because that one will
often swap between the charging and discharging state as it drains the
aux battery...).
PowerD: Use a cached timestamp when doing battery pull checks