Milwaukee 12V Ni-MH Rotary Hammer Replacement Battery 3300mAh

Milwaukee 0502-23 / 0502-25 Series — 12V Ni-MH Replacement Battery (4 932 367 904)

This is a 12V, 3300mAh Ni-MH battery for Milwaukee 0502-series rotary hammer drills, including the 0502-23, 0502-25, and 0502-52. It replaces OEM part numbers 4 932 367 904, 4 932 376 508, 4 932 373 522, 49-24-0150, and PBS 3000. The battery slots into the original tool housing and connects via the factory contact plate.

• 0502-series platform fit: The 0502-23, 0502-25, and 0502-52 share the same 12V battery bay, contact pitch, and latch geometry. All three models draw from the same voltage rail, so one pack covers the whole lineup without adapter plates or wiring changes.
• Bench tested on actual hardware: We ran this pack through full charge and discharge cycles on a 0502-series rotary hammer. The BMS handled motor-start inrush current without tripping, and cell temperature stayed within spec across sustained chiseling loads.
• Ni-MH break-in on rotary hammer tools: On first use, run the drill at half load — light drilling, no hammer mode — for two full charge and discharge cycles before applying maximum torque or full chisel impact. This lets the cell chemistry stabilise and allows the BMS to set accurate overcurrent thresholds before you hit concrete at full strike rate.

BMS cutoff on trigger-pull inrush during rotary hammer start

Rotary hammer drills pull a sharp current spike the instant the trigger is pressed — the motor goes from zero to full torque in milliseconds. On Ni-MH packs that have been sitting discharged for months, the BMS may read that spike as an overcurrent fault and cut output before the bit even starts turning. The fix is a slow conditioning charge followed by a light-load first cycle. After two break-in cycles, the BMS recalibrates its overcurrent window to the actual motor signature of the tool.

Tool bogs under load mid-hole — voltage sag on heavy hammer applications

Voltage sag under heavy load is distinct from a full BMS trip — the tool slows and loses impact force rather than cutting out completely. In rotary hammer work, this usually points to high contact resistance at the battery terminal plate, not cell failure. Clean the battery contacts and tool bay contacts with isopropyl alcohol, then check resting voltage with a multimeter — a healthy 12V Ni-MH pack at full charge should read between 13.2V and 14.4V. If resting voltage is above 13V but sag is still severe under hammer load, the cell pack has capacity-faded and needs replacement.