Insights: show averaged measured capacity with min/max instead of a single fluctuating reading

[almothafar]

Problem

The battery-health figure in Insights depends on a single, instantaneous capacity reading, which fluctuates between refreshes and can make health look jumpy or off.

getBatteryCapacity() computes chargeCounter / (percent * 10) from one live sample (SystemService.java:274-311), and measured health is currentFullMah / designMah from that one reading (BatteryHealthTracker.java:332-364). Both the current-capacity value and the health % it feeds move with each sample.

Request

Show an averaged measured capacity instead of a single snapshot, with the spread available as small secondary text. For example:

Measured capacity: 4500 mAh
avg of rated capacity (min/max: 4420 / 4580)

Suggested direction

• Collect capacity samples over time (e.g. a rolling set of recent readings, ideally sampled at similar charge levels since the estimate is noisier at some percentages) and store min / max / average.
• Drive the displayed capacity and the measured-health % from the average, not the latest sample, so both are stable.
• Show min/max as a small caption under the capacity value in Insights (BatteryInsightsActivity.java:106-110).
• Keep the existing unreliable-reading guard (issue Battery health: show 'Unknown' + tappable info when the charge gauge is unreliable (vs design capacity) #94) for devices with a broken charge counter.
• New strings need Arabic translations (values-ar).

Open questions

• How many samples / what window makes the average trustworthy without lagging real wear?
• Reset the running stats when the design capacity changes?