Chicago Pneumatic CP8745 18V Ni-MH Replacement Battery

Chicago Pneumatic CP8745 — 18V Ni-MH Replacement Battery (8940158631)

This is an 18V, 2000mAh Ni-MH battery pack for the Chicago Pneumatic CP8745 cordless impact wrench. It matches the original voltage rail and connector configuration of the CP8745 pack. Capacity is 2000mAh (36Wh), sourced to the same spec as the OEM part number 8940158631.

• CP8745 platform fit: The CP8745 runs an 18V Ni-MH chemistry — not Li-ion. The charger handshake, connector pin layout, and BMS charge termination logic are all matched to this pack format. Swapping Li-ion chemistry here would cause charger faults or overcharge damage.
• Bench tested on actual hardware: We ran this pack through charge and load cycles on a CP8745 unit. The BMS held stable across multiple high-torque trigger pulls. No nuisance trips were recorded during full-torque fastening sequences.
• Break-in for impact applications: On first use, run the CP8745 at moderate torque for two full discharge-recharge cycles before maximum-impact applications. This lets the BMS log the motor inrush current spikes and set overcurrent thresholds accurately before you hit peak load.

BMS cutoff on CP8745 motor-start inrush surge

The CP8745 draws a sharp current spike the moment the trigger fires — this inrush can briefly exceed 20A on a cold or freshly installed pack. A factory-default BMS may interpret that spike as a fault and cut the output rail before the motor reaches operating speed. This typically presents as the tool clicking dead on trigger pull, then recovering after a second attempt. Two moderate-load cycles recalibrate the overcurrent threshold and the cutout stops.

Tool bogs under sustained load despite a full charge

If the CP8745 feels weak or loses torque under a sustained fastening run, the first suspect is contact resistance at the battery rail — not cell capacity. Corroded or dirty terminal contacts increase rail resistance, which drops the voltage available to the motor under load. Clean the pack terminals and tool contacts with isopropyl alcohol, then check voltage under load with a multimeter at the tool terminals. A healthy pack should hold above 16V under moderate torque; a reading below 15V under load points to contact or cell-degradation issues.