About this replacement
Ryobi HP1201MK2 Series — 12V Ni-MH Replacement Battery (B-8286)
This is a 12V, 2100mAh Ni-MH battery replacing OEM part B-8286 in Ryobi 12V cordless drill/drivers. It fits the HP1201MK2, CTH1201, CTH1202, CTH1202K, and additional models in the Ryobi 12V platform. Total energy capacity is 25.2Wh.
- 12V platform compatibility: The HP1201MK2, CTH1201, and CTH1202 series share the same 12V rail, connector footprint, and BMS handshake protocol. A single pack services all of them without modification.
- Bench tested on actual hardware: We ran this pack through repeated trigger-pull cycles on the HP1201MK2. The BMS handled motor-start inrush current without tripping, and cell voltage held steady across load transitions.
- Ni-MH break-in on the HP1201MK2: On first use, run the drill at half load for two full discharge-charge cycles before applying maximum torque. This lets the BMS profile the motor's inrush draw and set accurate overcurrent thresholds before heavy fastening work.
BMS overcurrent trip on trigger-pull inrush in the HP1201MK2
The HP1201MK2 motor draws a spike of current the instant the trigger is pulled — this inrush can exceed the BMS's overcurrent threshold if the pack is cold or the cells are not yet profiled. A fresh Ni-MH pack has higher internal resistance until the cells have been cycled a few times, which amplifies the voltage sag during that initial spike. The BMS reads the sag as a fault and cuts power to protect the cells. Two break-in cycles at half load resolve this — internal resistance drops and the BMS recalibrates its cutoff threshold.
Charger won't accept the pack after it's been sitting unused
Ni-MH cells self-discharge during storage and can drop below 1.0V per cell — the point at which many Ryobi 12V chargers refuse to initiate a charge cycle. The charger reads the low voltage as a damaged or deeply discharged pack and blinks an error instead of starting. To recover it, briefly connect the pack to a compatible Ni-MH charger that has a recovery or trickle mode, allowing voltage to climb back above the acceptance threshold of approximately 10.8V for this 12V pack. Once the pack reaches that floor, the standard charge cycle resumes normally.