Panasonic EZ502 Cordless Drill Replacement Battery 2.4V 3000mAh

Panasonic EZ502 / EZ503 Series — 2.4V Ni-MH Replacement Battery (EZ902)

This is a 2.4V, 3000mAh Ni-MH replacement battery for the Panasonic EZ502 and EZ503 cordless drill/driver series. It also fits the EZ581, EY3652, and over 20 additional Panasonic compact power tool models. Capacity is drawn from product data — 3000mAh, 7.2Wh.

• EZ502 / EZ503 platform fit: These models share a 2.4V single-cell Ni-MH architecture with the same connector pitch and battery bay geometry. The charge termination logic uses delta-V detection, so the replacement cells must hit the same negative voltage slope at full charge — these do.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the EZ502 platform. The charger accepted the pack without fault codes, and the BMS reached termination cleanly without overcharge extension. Cell voltage held flat through mid-discharge before the expected Ni-MH drop-off.
• First two cycles on the EZ502: Run the drill at half load for the first two cycles before applying full torque. This lets the charger calibrate the delta-V termination point against the new cells and avoids a premature cutoff on the first high-draw trigger pull.

BMS overcurrent trip on motor-start inrush in the EZ502

The EZ502 motor draws a current spike at the moment the trigger is pulled — inrush current can be three to five times the steady running load. On a new or cold Ni-MH pack, internal resistance is temporarily elevated, which amplifies the voltage sag at the terminals during that spike. If the BMS reads the sag as an overcurrent event, it cuts the output before the motor reaches running speed. Two conditioning cycles at half load lower the internal resistance and shift the BMS threshold recognition into the normal operating window.

Drill bogs under load and loses torque mid-screw

This is voltage sag — not a dead cell. When the EZ502 drives a fastener into dense material, sustained current draw pulls the pack voltage below the tool's low-voltage cutoff. The result feels like the drill losing power halfway through a drive. Check the battery rail contacts first — oxidation on the terminal strips adds resistance and worsens sag under load. Clean contacts with isopropyl alcohol, reseat the pack, and retest; if sag continues, the cells need a full discharge-recharge cycle to recover resting voltage above 2.3V.