1. The charge falls much faster than before
Lithium-ion batteries gradually lose capacity through age, heat and charge cycles. If a phone that once lasted a full day now needs charging by lunchtime under the same usage, the battery may be worn.
Check battery usage in Settings first. A newly installed app, weak mobile signal, background location service or a major software update can also increase consumption. Compare several normal days instead of judging one unusually busy day.
2. The percentage jumps or the phone shuts down
Unexpected shutdowns at 20% or 30%, large percentage jumps and restarts during camera or gaming use can occur when an ageing battery cannot supply peak power. A diagnostic test can separate a weak battery from software, charging-port or board faults.
3. Charging has become unreliable
Slow charging is not always a battery problem. Inspect the cable and adapter, carefully check the port for compacted lint, and test a known-good compatible charger. Stop if the plug, cable or phone becomes abnormally hot.
If charging works only at an angle, the port or cable may be damaged. If the percentage rises normally but disappears quickly after unplugging, battery health becomes a stronger suspect.
4. Performance is reduced
Some phones manage performance when the battery can no longer deliver stable peak power. You may notice slower app launches, reduced frame rates or brief freezes. Storage that is nearly full and demanding software can cause similar symptoms, so diagnosis matters.
5. The phone is unusually hot
Warmth during fast charging, navigation or gaming can be normal. Persistent heat during light use, heat while idle or a sudden temperature change deserves attention. Remove the case, disconnect the charger and let the phone cool on a non-flammable surface.
6. The battery-health reading is low
Many phones provide a battery-health or diagnostic reading. It is a useful indicator, not the complete diagnosis. Capacity, internal resistance, temperature and real-world stability all matter. A battery below the manufacturer’s service threshold combined with poor runtime is a strong reason to request an assessment.
7. The screen or back is lifting
A swollen battery can push the display or rear cover away from the frame. This is a safety issue, not a cosmetic fault. Switch the phone off, do not press the panel flat, do not puncture it and do not charge it. Keep it away from heat and arrange professional handling promptly.