Battery Troubleshooting
Edit on GitHubDiagnosing beacon battery faults: fast drain, no charge, sagging under TX, and the measurements that find the cause.
Battery Troubleshooting
Battery faults look like every other fault: the beacon resets, the range drops, the runtime collapses. This page is the isolation sequence.
The symptom map
| Symptom | Likely cause |
|---|---|
| Runtime collapsed | Cell aged, or something not sleeping (see Sleep Current) |
| Resets during TX | Cell sagging under the burst (see Cold Weather Batteries) |
| Won’t charge | TP4056 input problem, or dead cell |
| “Low battery” with full cell | Cold, or wrong thresholds for the chemistry |
| Hot cell during charging | Charger fault, or cell damaged: STOP using it |
The measurements
- Resting voltage: 4.2 V charged, 3.7 V nominal, below 3.0 V is dead (protected cells cut off first, see Protected vs Unprotected).
- Voltage under load: watch the voltage while the beacon transmits; a healthy cell dips less than 0.3 V, a tired cell dips 0.5 V+ and can brown out the ESP32.
- Sleep current: see Power Measurement; above 1 mA in sleep is a board problem, not a cell problem.
The sag test
The definitive test for a tired cell:
- Charge fully and rest 30 minutes.
- Note the resting voltage.
- Enable a continuous TX test (or the emergency interval).
- If the voltage drops below 3.3 V during the burst, the cell cannot deliver the current: replace it.
Cell replacement rules
- Same chemistry and protected type (see Protected vs Unprotected).
- Never mix new and old cells (see Parallel Cells).
- Dispose of damaged cells properly; a swollen cell is a fire risk, not a battery.
Related pages
- Battery Monitor Details for the firmware side
- Charging and Cell Care for the charger
- Power Measurement for the procedure