Black & Decker A9251 9.6V Cordless Drill Replacement Battery 1500mAh

Black & Decker CD231 Series — 9.6V Ni-MH Replacement Battery (A9251 / PS120)

This is a 9.6V, 1500mAh Ni-MH battery pack for the Black & Decker CD231 cordless drill/driver and related models including the CD231K, CD231P8, and CD9600. It replaces OEM part numbers A9251, PS120, and PS120A. The pack slots into the same battery bay as the original and connects to the same charging circuit.

• CD231 family compatibility: The CD231, CD231K, CD231P8, and CD9600 all share the same 9.6V battery bay, slide-lock connector, and charge port wiring. One pack covers all of them because the voltage rail and connector geometry are identical across the lineup.
• Bench tested on actual hardware: We cycled this pack through a full charge and three load draws on a CD231 drill. The BMS held stable through repeated trigger pulls and showed no false overcurrent trips during normal driving torque.
• Motor inrush break-in: On the first two uses, run the drill at half load — driving small screws or light drilling — before full-torque applications. This gives the BMS time to log the motor's inrush current signature and set accurate overcurrent thresholds before you push the pack hard.

BMS cutoff on trigger-pull inrush in the CD231

When you pull the trigger on a cordless drill, the motor draws a sharp current spike before it reaches operating speed. On a fresh or just-installed Ni-MH pack, the BMS may read that spike as an overcurrent event and cut power before the bit turns. This is more likely in cold conditions where cell internal resistance is higher, which amplifies the apparent voltage sag during inrush. If the drill cuts out on the first pull but recovers after a few seconds, the BMS tripped and reset — not a defective pack. Two or three half-load cycles train the BMS to the CD231's actual inrush profile and stop false trips.

Charger not recognising the new pack after storage

Ni-MH packs lose voltage during storage, and some Black & Decker chargers won't begin a charge cycle if the pack voltage reads below their acceptance threshold — typically around 7V for a 9.6V pack. The charger light stays off or blinks without progressing. To recover the pack, try a different charger that accepts low-voltage packs, or briefly connect the battery to a known-good unit that will trickle charge below threshold. Once the pack climbs above 7.5V, the standard charger will accept it and run a full charge cycle normally.