Symptoms
- Battery percentage drops suddenly from a stable number, like 30% to 5%
- Phone shuts down while showing double-digit battery left
- Percentage jumps up or down erratically
- Battery seems to last unpredictably from day to day
Likely causes
- CommonReduced battery health making voltage readings less stableAn aged battery's voltage curve becomes less predictable, causing the percentage estimate to jump.
- CommonCold temperature affecting voltage readoutBatteries read lower in cold weather and can recover once warmed, causing apparent jumps.
- PossibleA battery calibration mismatch after months without a full dischargeThe percentage estimate can drift from the true charge level over time.
- Less commonSoftware glitch in battery reportingA stuck battery statistics service can misreport level until reset.
What to do
- Check Settings > Battery > Battery Health & Charging for the maximum capacity percentage.
- Note whether jumps happen more in cold weather, which is often the simple explanation.
- Let the phone run down to shutdown once, then charge fully to 100% uninterrupted to help recalibrate.
- Avoid cases or environments that keep the phone very cold when this happens outdoors.
- Update to the latest iOS version, since battery reporting bugs are sometimes patched.
- Restart the phone to reset battery statistics tracking.
- If jumps happen regularly and capacity is below 80%, treat it as a sign of battery wear.
- Keep a rough log of when it happens if considering a battery replacement, to show a technician.
When to call a pro
If percentage jumps are frequent and battery health is low, a battery replacement usually resolves both the drain and the inaccurate readings.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.