Symptoms
- Battery percentage suddenly drops from a high number to much lower
- Percentage jumps up after a restart
- Battery estimate seems inconsistent between charges
- Watch dies unexpectedly while still showing charge remaining
Likely causes
- CommonBattery percentage calibration driftSoftware estimates of remaining charge can drift out of sync with actual battery level over time.
- PossibleCold temperatures affecting battery voltage readingsBatteries read lower in cold weather even if actual capacity is fine.
- PossibleAging battery with less predictable discharge curveOlder batteries can behave less linearly as they degrade.
- Less commonSoftware bug in the battery reporting systemOccasionally a firmware bug misreports percentage until fixed in an update.
What to do
- Let the watch fully charge to 100% and then run it down close to empty once, which can help recalibrate the percentage estimate.
- Avoid frequent partial charges for a cycle or two if you're trying to diagnose calibration drift specifically.
- Update the watch's firmware, since battery reporting bugs are periodically patched.
- Note if jumps happen mostly in cold weather, which is a normal battery chemistry effect rather than a fault.
- Restart the watch, which can reset the battery estimation software.
- If the watch is older, compare current runtime to when it was new to judge real capacity loss versus a reporting glitch.
When to call a pro
If the watch also shows real symptoms like dying much earlier than the displayed percentage suggests, and it's over a year old, the battery has likely degraded and needs replacement.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.