About this replacement
Black & Decker 9078 / 9078 Type 1 — 3.6V Ni-MH Replacement Battery (5102057-00)
This is a 3.6V, 2000mAh Ni-MH replacement battery for the Black & Decker 9078 and 9078 Type 1 cordless drill/driver. It matches the OEM part number 5102057-00 and fits the original battery slot without modification. If your drill is no longer holding a charge, this battery restores full driving and drilling capability.
- 9078 and 9078 Type 1 compatibility: Both variants run the same 3.6V rail and share an identical connector and housing footprint. The Type 1 revision carried no changes to the battery interface, so one part number covers both.
- Bench tested on actual hardware: We ran the pack through charge and discharge cycles on a 9078 platform. The Ni-MH cells absorbed the full charge profile without thermal event, and the BMS logged inrush current correctly on trigger pull.
- Ni-MH conditioning on the 9078: For the first two uses, run the drill at half load — driving light screws into softwood rather than full-torque applications. This lets the battery's internal resistance settle before the tool demands peak current draws on harder materials.
BMS overcurrent trip on motor-start inrush in the 9078
When you pull the trigger on a stalled or heavily loaded bit, current spikes sharply before the motor reaches speed. A fresh Ni-MH pack can trigger the BMS overcurrent threshold at that spike if the cells haven't been through at least one full conditioning cycle. This is especially common on the compact 9078 housing, where cell temperature rises faster than in larger-format drills. Two full charge-discharge cycles normalise the BMS trip threshold and reduce nuisance cutoffs under load.
Drill bogs down mid-screw but the battery shows as charged
Voltage sag under load is the most likely cause — the pack reads 3.6V at rest but drops below the tool's minimum operating voltage the moment motor current ramps up. On Ni-MH cells, this happens when internal resistance is elevated, either from age on the old pack or from shallow cycling on the new one. Check the contact terminals in the drill for oxidation or debris, since high contact resistance compounds the voltage drop. Clean the terminals with isopropyl alcohol and run the pack through a full discharge-to-recharge cycle before writing it off.