Quick answer: check solar input, charging permissions and nightly demand
A battery that does not reach full charge may have insufficient solar input, a wiring or controller fault, a temperature or BMS restriction, or a nightly load that exceeds the energy available each day. The useful first step is to distinguish no charging from some charging but an ongoing energy deficit. A voltage reading alone does not reliably establish LiFePO4 state of charge.
Use the controller and battery manuals for the exact model. A qualified technician should isolate circuits and perform electrical tests using the specified sequence, instruments and protection. Do not bypass the BMS, connect an LED module directly to a battery, or use a generic charger or voltage threshold. Stop using a damaged, swollen, leaking or unusually hot battery and arrange service.
1. Record the symptom before changing settings
- Identify the light, controller, panel and battery model numbers; photograph their labels.
- Record controller status, fault codes, reported battery temperature and any charge-current history.
- Note when the problem started, recent weather, panel shading or dirt, and whether the night profile was changed.
- Check whether one unit or multiple units show the same behaviour.
2. Check the solar input
Inspect the panel from a safe accessible position for shading, heavy contamination, damage and changed orientation. A panel can show voltage while supplying little useful power. Comparing voltage alone with a battery reading will not prove that charging current is flowing. A technician should compare the actual PV input and current with the controller manual under recorded sunlight conditions.
Connections, cable damage, polarity, protective devices and water ingress should be inspected with circuits isolated according to the service manual. Do not unplug live connectors as a shortcut to testing.
3. Check whether charging is permitted
Read the controller and BMS indications before assuming that either has failed. Battery temperature, protective limits, an incompatible charging profile or a communication fault may prevent charging. The permissible charging temperature can differ from the discharge temperature. Use the battery specification and controller configuration for the model; keep protection enabled.
4. Separate a fault from an energy deficit
| Observation | Evidence to collect | Next step |
|---|---|---|
| No reported PV input in good sunlight | Panel condition, controller code, input measurements by a technician | Check the PV circuit and controller against the manual |
| PV input present but charge restricted | BMS state, battery temperature, charge settings | Resolve the documented restriction or service fault |
| Charging occurs but charge falls over successive days | Daily incoming energy and nightly load profile | Review solar sizing, shading and recovery time |
| Charge is reported full but night operation is short | Load history, usable-capacity test and cutoff reason | Check unexpected loads, battery condition and protection events |
5. Calculate the load using actual power
For an illustrative 40 W light drawing 40 W for 3 hours, 20 W for 4 hours and 10 W for 5 hours, lighting consumes 250 Wh per night. Controller, communication and heating loads must be added. These are assumed electrical powers; a dimming percentage does not necessarily produce the same power percentage. Compare incoming and consumed energy at compatible measurement boundaries.
A larger battery can increase stored energy, but it will not solve a persistent daily charging deficit. The panel must cover the load and recover the battery after poor weather. See the rainy-day backup guide and battery selection guide.
When to request technical support
Send model labels, controller codes, current settings, dates and times, installation photos and several days of charge/load history if available. Include recent weather and the number of affected units. This helps separate a site-wide energy issue from a component fault.
Send diagnostic information to MCL Solar. For night-side symptoms, see dim or unlit solar street light troubleshooting.
Reference
Manufacturer example of LiFePO4 operating and charging limitations. Apply the manual supplied with your own battery and controller.