Kobalt K18-NB15A 18V Replacement Battery 2500mAh Ni-MH

Kobalt K18-NB15A — 18V Ni-MH Replacement Battery (0005667)

This 18V 2500mAh Ni-MH battery replaces the Kobalt 0005667 pack used across Kobalt 18V cordless power tools, including drills, impact drivers, and circular saws. It matches the original voltage rail and connector configuration. Capacity is 2500mAh (45Wh) — drawn from the product spec, not estimated.

• K18-NB15A platform fit: The 18V Ni-MH cell stack and connector pinout on the K18-NB15A series are consistent across drills, impact drivers, and saws in that line — they share the same voltage rail and terminal layout, so one battery services the full 18V platform.
• Bench tested on actual hardware: We cycled this pack through a drill and an impact driver under load. The BMS held voltage through repeated trigger pulls and flagged no overcurrent faults during normal torque application. Cell temperature stayed within spec across the test cycles.
• First-use conditioning on 18V Ni-MH tools: Run the tool at half load for the first two cycles before full torque applications. This lets the BMS profile the motor inrush current draw before locking in its overcurrent protection thresholds — skipping this step can cause nuisance cutoffs on heavy initial loads.

BMS cutoff on motor-start inrush in 18V drills and saws

When you pull the trigger on a drill or circular saw, current draw spikes sharply for a fraction of a second before the motor reaches running speed. On a fresh or cold Ni-MH pack, that inrush spike can exceed the BMS overcurrent threshold and cut power before the tool even starts moving. Ni-MH cells have higher internal resistance than Li-ion, which amplifies the voltage sag during that surge. If the BMS trips, release the trigger completely, wait three seconds, then re-engage at half speed to reset the protection circuit.

Tool bogs under sustained load and then cuts out

This is a thermal cutoff event, not a weak battery. Under sustained heavy load — long drill bits in hardwood, full-depth circular saw cuts — both the motor and the Ni-MH cells generate heat inside an enclosed housing. When cell temperature hits the BMS thermal cutoff threshold, the pack shuts down to prevent damage. Set the tool down and let the pack rest for ten minutes before resuming. If it happens repeatedly on moderate loads, check that the battery contact rail is clean and seated fully — dirty contacts raise resistance and accelerate heat buildup at the terminal.