`battery`

The battery, from UPower: its combined display device, followed live, and every power source it reports.

Field	Type
`present`	`bool`	A battery is present: `if battery.present { Battery }`.
`percent`	`float`	Charge, 0 to 1: `pct(battery.percent)`.
`charging`	`bool`	It is charging.
`time_left`	`duration?`	Time until empty, or until full while charging; null when unknown.
`icon`	`text`	An icon name for its charge and state.
`power`	`float`	Power draw in watts.
`devices`	`[PowerDevice]`	Every power source but line power, keyed by `id`: laptop batteries and the batteries of peripherals.

Method

fn history(span: duration, points: int = 60) -> Async<[float]> The battery's charge over the last span, as UPower recorded it (GetHistory, which UPower keeps across reboots): points charges, 0 to 1, evenly spaced from span ago to now, oldest first, so a chart shows the hours before the shell started: let past = battery.history(10800s) ?? []. Each is the charge last recorded at or before its time; the times before UPower's first record in the span are left out, so the list may be shorter (it still ends now). Of the laptop's first battery that keeps a history; an error when none does. Asked only when called, never polled. points is at most 2000.

Method
`fn history(span: duration, points: int = 60) -> Async<[float]>`	The battery's charge over the last `span`, as UPower recorded it (`GetHistory`, which UPower keeps across reboots): `points` charges, 0 to 1, evenly spaced from `span` ago to now, oldest first, so a chart shows the hours before the shell started: `let past = battery.history(10800s) ?? []`. Each is the charge last recorded at or before its time; the times before UPower's first record in the span are left out, so the list may be shorter (it still ends now). Of the laptop's first battery that keeps a history; an error when none does. Asked only when called, never polled. `points` is at most 2000.