About this replacement
Panasonic EY3760B Series — 21.6V Li-ion Replacement Battery (EY9L60)
This is a 21.6V, 4000mAh Li-ion battery pack replacing the OEM EY9L60, EY9L60B, EY9L61B, and EZ9L61 units. It fits the Panasonic EY3760B cordless impact driver and compatible EY7460 series models. The 86.4Wh rating keeps the pack in the same energy class as the factory unit.
- EY3760B and EY7460 series compatibility: These models share a common 21.6V rail, the same battery connector footprint, and a matching BMS handshake protocol — so one pack covers the full lineup without adapter or firmware changes.
- Bench tested on actual hardware: We cycled this pack through repeated high-torque trigger pulls on an EY7460 spindle. The BMS held steady through motor-start inrush spikes and did not trip into overcurrent cutoff under sustained fastening loads.
- Impact driver break-in procedure: On first use, run the tool at half torque for two full cycles before pushing maximum fastening loads. This lets the BMS profile the motor's inrush current draw and set accurate overcurrent thresholds before you hit structural fixings.
BMS overcurrent trip on trigger-pull inrush surge
Impact drivers draw a short, sharp current spike the moment the motor starts — often two to three times the steady-state draw. A new or freshly charged pack has tight overcurrent thresholds until the BMS has seen several real load cycles. If the pack shuts down on the first hard trigger pull, it is not a faulty cell — the BMS has not yet calibrated to this motor's inrush signature. Run two light-load cycles first, and the threshold self-adjusts to allow normal operation.
Charger shows blinking red on a pack that sat in storage
Li-ion cells drop below the charger's acceptance threshold — typically around 2.5V per cell — after several months without use. Most Panasonic chargers refuse to charge below this floor and signal the problem with a blinking or solid red LED. The fix is a brief pre-charge pulse: leave the pack on the charger for 20–30 minutes without removing it, and most chargers will step through a recovery mode automatically. If the red light persists beyond 30 minutes, check individual cell voltage — any cell reading under 2.0V needs replacement before charging continues.