Würth 700900320 12V Ni-MH Replacement Battery 2000mAh

Würth BS12A Power — 12V Ni-MH Replacement Battery (700900320)

This is a 12V 2000mAh Ni-MH replacement battery for the Würth BS12A Power cordless drill. It replaces OEM pack 700900320 and slots into the same battery bay without modification. Capacity is 2000mAh (24Wh), matching the original specification.

• BS12A Power platform fit: The BS12A Power uses a 12V Ni-MH pack with a specific cell arrangement and connector orientation. Ni-MH chemistry suits this older platform — the tool's charger circuit and BMS handshake are calibrated for Ni-MH voltage curves, not lithium chemistry, so substituting a Li-ion pack here would cause charge faults or refusal.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge runs on a 12V drill platform. The BMS held stable across motor-start inrush spikes and sustained the nominal voltage rail through repeated trigger pulls without tripping overcurrent protection.
• Ni-MH first-use conditioning: Run the drill through two full discharge-to-charge cycles before heavy applications. Ni-MH cells deliver noticeably lower capacity on the first cycle — the chemistry requires a few full cycles to reach rated capacity, unlike lithium packs which are at or near full capacity immediately.

BMS cutoff on the BS12A Power during motor-start inrush

When you pull the trigger on a 12V drill, the motor draws a brief inrush current that can be three to five times the running current. On a new or cold Ni-MH pack, internal resistance is higher than on a warmed pack, which amplifies the voltage sag at that moment. If the sag drops the rail far enough, the BMS reads it as an overcurrent event and trips. Letting the pack warm to room temperature before use, and starting with partial trigger pressure, keeps the inrush spike within the BMS acceptance window.

Charger not recognising the pack after extended storage

Ni-MH packs self-discharge at roughly 1–2% per day at room temperature. After several months on the shelf, a pack can fall below the voltage floor the charger uses to detect a valid battery — the charger sees a dead cell signature rather than a depleted-but-good pack. Some Würth chargers allow a recovery or trickle-charge mode; engage that first. If no recovery mode is available, a brief boost from a compatible lab charger to 11V is enough to push the pack back above the charger's acceptance threshold, typically around 10.5–11V for a 12V Ni-MH pack.