About this replacement
CATEYE HL-EL625RC — 3.7V Li-ion Replacement Battery (BA-625)
This is a 3.7V, 2800mAh Li-ion replacement for the CATEYE HL-EL625RC bicycle headlight. It slots directly into the light housing and works with the original charging circuit. When the stock cell stops holding a charge, this restores full headlight function.
- HL-EL625RC compatibility: The BA-625 uses the same voltage rail and physical footprint as the factory cell. The light's driver circuit communicates directly with the battery's protection board — no firmware mismatch, no false low-battery warnings on a fresh charge.
- Bench tested on actual hardware: We ran this cell through the HL-EL625RC's full charge cycle. The BMS accepted charge without interruption, cell voltage reached 4.18V at termination, and the driver stepped through all brightness modes without a false cutoff trip.
- Pre-ride charge habit for the HL-EL625RC: Charge the light fully before a night ride. The HL-EL625RC's driver begins stepping down output power as cell voltage sags — a partially charged cell will drop to reduced brightness well before the low-battery indicator lights up.
Why the HL-EL625RC dims before the low-battery indicator appears
The HL-EL625RC uses a constant-current driver that monitors cell voltage in real time. As the Li-ion cell discharges from 4.2V toward 3.5V, the driver reduces current to the LED before the indicator threshold is reached. This is normal driver behaviour, not a fault. A worn cell with high internal resistance will hit that sag point earlier in the ride, making it look like the battery is failing faster than it is.
Light not reaching rated lumen output after battery replacement
If the headlight runs noticeably dimmer than expected after fitting a new cell, check that the battery reached a full charge before use — the driver needs cell voltage above 4.0V to sustain maximum brightness mode. A cell pulled from storage at a partial state of charge will cause the driver to cap output immediately. Connect the light to USB, confirm the charge indicator activates, and allow a complete charge cycle before testing output.