Charging While Off

Definition

A device that can charge while off can continue charging its battery when it is powered down (screen off, OS not running).

In practice, this is the general rule for many battery-powered devices. The important exceptions are:

• some devices auto-boot when power is connected, so they do not reliably stay off while charging
• some devices cannot be turned off, so an off-state session is not possible
• some devices only charge while off, meaning they must be powered down to accept charge

How the app should decide ON vs OFF

When information is available, the app should decide the charging mode automatically:

• If the available information clearly indicates ON or OFF, use it.
• If the information indicates multiple plausible variants, show a non-intrusive hint that the user should specify whether the session is ON or OFF.
• If no information is available, the app assumes ON for devices that support both ON and OFF charging (for capacity learning and confidence rules).

Why it matters for battery capacity estimation

Off-state charging sessions tend to produce the cleanest signal for estimating battery capacity (energy stored):

• Most of the measured input energy goes into the battery, instead of being consumed by the device itself.
• The result is less affected by background processes, radios, thermal throttling, screen usage, and OS-level behavior.

App implications

Defaults

• Default assumption (for capacity learning): if the user does not specify otherwise, a device is treated as on/unknown-state while charging.

Capacity estimation priority (conceptual rule)

When we have both:

• high-confidence capacity determinations from off-state charging, and
• lower-confidence determinations from on/unknown charging,

then:

• off-state determinations are preferred for establishing the device’s capacity baseline
• on/unknown determinations must not overwrite off-state determinations, except when they imply a smaller capacity
  • example: the user logs a large measured energy, but later battery-percent checkpoints indicate the battery can’t actually hold that much energy (or has degraded), so we allow the estimate to move downward

Current implementation note

For devices that are not marked as chargeable while off, the app does not accept sessions that end at “full” as capacity inputs (near-full can hide unknown “top-off” time/energy while the OS is doing its own work). For devices marked as chargeable while off, full / near-full sessions remain eligible.

Device-specific notes (practical guidance)

• iPhone: tends to auto-boot when connected to a charger. To record an off-state session, you may need to shut it down after connecting power. Some factors can still trigger a boot even if the phone was shut down.
• Powerbank: treat as “chargeable only while off” (no active output load). For capacity learning, prefer sessions where the powerbank is not simultaneously powering other devices.
• AirPods case: treat as “off” only if the earbuds are not inside the case while charging (otherwise the case is also charging the earbuds).
• Apple Watch: cannot be reliably powered down for charging; treat as always on.
• Garmin Edge bike computers / some Garmin watches: treat as chargeable only while off (they need to be powered down to charge).