Stanley 18V FMC687L Replacement Battery 4000mAh Li-ion

Stanley FMC625D2 / FMC645D2 Series — 18V Li-ion 4000mAh Replacement Battery (FMC687L)

This is an 18V Li-ion replacement battery rated at 4000mAh (72Wh), built to the FMC687L specification. It fits a broad range of Stanley 18V cordless tools including the FMC625D2, FMC645D2, FMC675B, and FMC675B-XE, plus twelve additional models in that platform. The connector and BMS handshake match the original pack, so the charger and tool recognise it without modification.

• FMC625D2 / FMC645D2 platform compatibility: These models share the same 18V rail, slide-in connector block, and BMS communication protocol. One pack works across drills, impact drivers, and saws in this series without adapter or re-pairing.
• Bench tested on actual hardware: We ran this pack through motor-start inrush cycles on a drill and a circular saw. The BMS held through the trigger-pull voltage spike both times and did not trip the overcurrent threshold under normal load.
• Break-in procedure for this platform: On first use, run the tool at half load for two cycles before any maximum-torque application. This allows the BMS to profile inrush current draw and set accurate overcurrent thresholds before you push the motor hard.

BMS cutoff on motor-start inrush surge with the FMC625D2

When you pull the trigger hard from a dead stop, the motor draws a spike of current that can be three to four times the running draw. On a new or recently stored pack, the BMS may not yet have a calibrated overcurrent threshold for that motor, so it cuts the circuit as a precaution. This is not a faulty battery — it is the protection logic responding to an uncalibrated load profile. Two half-load break-in cycles let the BMS log the inrush pattern and widen its threshold to match the motor.

Charger blinking red and refusing to accept the pack after storage

Stanley's 18V charger has a minimum acceptance voltage — typically around 12V. If a pack sits unused for several months, self-discharge can pull cell voltage below that floor and the charger blinks red instead of beginning a charge cycle. The fix is a brief recovery charge using a compatible charger that supports a wake-up or trickle mode, which nudges the cells back above 12V before the main charge begins. If no trickle mode is available, some users have success connecting the pack for 30-second intervals repeatedly until the charger accepts it. Once cell voltage clears the acceptance threshold, the charger should switch to its normal green charging state.