Kraftixx 18V 4000mAh Replacement Battery 4514071

Kraftixx KX-RS 18 Li Solo — 18V Li-ion Replacement Battery (4514071)

This is an 18V, 4000mAh (72Wh) lithium-ion replacement battery for the Kraftixx KX-RS 18 Li Solo and compatible 18V cordless tools. It replaces OEM part numbers 4514071 and 4514072. Fits the KX-AHS 1858 Li Solo, KX-AKS 1825 Li Solo, KX-ARM 3637 Li, and additional models in the same 18V Kraftixx line.

• Shared 18V platform compatibility: These Kraftixx models run on the same 18V battery rail, use the same connector housing, and communicate with the same BMS handshake protocol. One battery works across the range because the voltage threshold and discharge curve match across each tool's motor controller.
• Bench tested on actual hardware: We cycled this pack through full discharge and recharge sequences on a compatible 18V Kraftixx platform. The BMS responded correctly to motor-start inrush, maintained stable voltage under sustained load, and triggered thermal protection at the expected threshold without nuisance cutoffs.
• First-use break-in on high-torque applications: Run the tool at half load for the first two cycles before applying maximum torque. This lets the BMS profile the motor's inrush current draw and calibrate overcurrent protection thresholds before you push the pack hard.

BMS cutoff on motor-start inrush surge in the KX-RS 18 Li Solo

When you pull the trigger on a loaded drill or saw, the motor draws a spike of current — often three to five times the running current — in the first milliseconds of startup. A new battery's BMS has no stored profile of that motor yet, so its overcurrent threshold may trip on that spike before the motor even reaches speed. This is more common if the battery sat in storage before first use, because the BMS resets its learned parameters after a long rest period. Running two partial-load cycles before full-torque work gives the BMS time to set a realistic overcurrent window for your specific tool's motor.

Charger shows blinking red light and won't accept the new pack

This happens when a battery arrives from storage with cell voltage below the charger's acceptance threshold — typically under 2.5V per cell on an 18V Li-ion pack. The charger reads the pack as faulty rather than depleted and refuses to enter bulk charge mode. To recover the pack, most Kraftixx chargers support a trickle or "wake-up" mode: leave the battery on the charger for 15–30 minutes without interrupting the connection. Once cell voltage climbs above the acceptance floor — around 2.8V per cell — the charger will switch from blinking red to normal charging status.