Latch the low-battery warning until the battery recovers

[djbarrios]

What happens

While the notebook discharges near the 10% threshold, the low-battery service fires the critical "Time to recharge! / Battery is down to 10%" notification over and over — dozens of identical copies. They are sent with -u critical, which never auto-expires (-t 30000 is ignored for critical urgency), so they stack up and stay on screen until dismissed one by one.

Cause

shell/plugins/services/battery/BatteryModel.js → shouldWarnLowBattery() sets

notifiedLowBattery: low

where low requires the device to be currently discharging and <= threshold. Any moment UPower does not report "discharging" — a briefly engaged charger, a weak dock, an energy-rate blip, a pending-charge/unknown state — makes low false and clears the latch. Service.qml polls every 30 s (and on every onOnBatteryChanged), so the next tick sees alreadyNotified == false again and re-fires the warning. There is no hysteresis or recovery check, so a battery parked around 10% with a marginal power source produces an unbounded stack.

Fix

Keep the latch set once the warning has fired until the battery genuinely recovers to threshold + 10. The warning then fires once per discharge episode and re-arms only after a real recovery. Transient non-discharging states at a low percentage no longer reset it.

Tests

test/shell.d/battery-test.sh gains coverage for:

• the latch holding through a non-discharging blip at a still-low level
• the latch holding above the threshold but below the re-arm level
• the latch clearing once the battery recovers to the re-arm level

./test/shell passes (the 3 unrelated failures on my machine — config-test, snapper-test, unowned-system-paths-test — also fail on a pristine checkout here; they check the live system, not the shell code).

Repro

Let the battery run down to ~10% with an intermittently connected charger or a weak dock, or on a system whose UPower state flaps near empty, and watch the notifications pile up.

[djbarrios]

[spuder]

Thank you for opening this issue, this has been one of the more annoying bugs.