About this replacement
Makita 12V Max CXT Series — 12V Li-ion 2500mAh Replacement Battery (BL1041B)
This is a 12V Li-ion replacement battery rated at 2500mAh (30Wh) for the Makita 12V Max CXT platform. It fits compact cordless drills, drivers, circular saws, and other handheld CXT tools including the CT226, SH02R1, and DT03R1. OEM part numbers covered include BL1041B, BL1040B, BL1021B, BL1020B, BL1015, BL1016, BL1021, BL1040, and BL1041.
- CXT platform compatibility: All listed models share the same 12V rail, slide-in contact geometry, and BMS communication protocol. Any tool running a BL1040-family pack accepts this cell stack without modification to the terminal interface or charge circuit.
- Bench tested on actual hardware: We ran this pack through a CT226 drill driver and a DT03R1 impact driver. The BMS held steady through repeated trigger-pull inrush spikes and balanced cell voltage within 20mV across the stack after each discharge cycle.
- CXT motor inrush conditioning: On first use, run the tool at half load for two cycles before full-torque applications. This lets the BMS log the motor's inrush current signature and set overcurrent thresholds before you drive the pack into maximum draw.
BMS overcurrent trip on motor-start inrush in CXT drills and drivers
Compact 12V tools draw a short but steep current spike the moment the motor starts — often 3 to 5 times the steady running current. On a new or recently stored pack, the BMS overcurrent threshold may not yet be calibrated to the specific motor profile. If the inrush spike exceeds the default threshold, the BMS trips and cuts output before the tool reaches full speed. Running two partial-load cycles first trains the BMS to recognise the motor's start signature and raises the trip threshold accordingly.
Pack drops out under sustained circular saw or high-torque load
Sustained heavy cuts generate heat in both the motor and the cell stack simultaneously. In the enclosed CXT battery housing, that heat has limited escape. Once cell temperature exceeds the BMS thermal cutoff point — typically around 60°C — the pack disconnects to protect the cells. The tool stops mid-cut even though the pack appears charged. Let the pack cool for 10 minutes in open air, then check the resting voltage at the terminals — it should read between 12.0V and 12.6V before resuming work.