About this replacement
Panasonic EY7880 Series — 28.8V Li-ion Replacement Battery (EY9L80)
This is a 28.8V, 2000mAh (57.6Wh) Li-ion battery pack for the Panasonic EY7880 cordless impact driver. It fits the EY7880LN2C, EY7880LN2S, EY7880LN2T, and related variants sharing the EY9L80 OEM part number. Voltage and connector match the original pack exactly.
- EY7880 series compatibility: These models share the same 28.8V rail, slide-in connector format, and BMS communication protocol. A pack that passes the handshake on one will pass on all variants in this lineup.
- Bench tested on actual hardware: We ran this pack through motor-start inrush cycles on the EY7880 platform. The BMS tracked overcurrent events without nuisance tripping and held the voltage rail steady through repeated fastening sequences.
- Break-in on first use: Run the driver at moderate torque for two full discharge-and-charge cycles before pushing maximum torque settings. This lets the BMS log the motor's inrush current signature and set accurate overcurrent thresholds before heavy-load work begins.
BMS cutoff on trigger pull during impact driver motor-start inrush
The EY7880 impact driver draws a sharp current spike the instant the trigger is pulled — this inrush can briefly exceed 20A before the motor reaches operating speed. A new or storage-depleted pack may trip the BMS overcurrent threshold during this spike, cutting power immediately. The fix is to let the BMS complete two or three partial load cycles so it can distinguish a normal inrush spike from a genuine fault. If cutouts persist after break-in, check rail contact resistance — oxidised contacts increase the voltage drop during inrush and push the BMS closer to its trip threshold.
Charger refusing to accept the pack after extended storage
Li-ion cells left unused for several months can drop below the charger's acceptance voltage floor, typically around 2.5V per cell. When the Panasonic charger sees a pack below that threshold, it flashes an error and refuses to begin a charge cycle. Some chargers have a recovery or "wake" mode — engage it by holding the pack in the charger for 10–15 minutes before the main charge starts. If the charger has no wake mode, a brief pulse charge to bring each cell above 2.8V is enough to get the pack past the acceptance check.