About this replacement
Motorola Mag One BPR40 / A8 / A6 — 7.5V Ni-MH Replacement Battery (PMNN4071)
This 7.5V, 1700mAh Ni-MH pack replaces the OEM battery on the Motorola Mag One BPR40, A8, and A6 portable two-way radios. It matches the original form factor, connector, and BMS handshake profile. Part numbers PMNN4071, PMNN4071A, PMNN4071AR, and PMNN4071AC all apply to the same physical pack.
- BPR40 / A8 / A6 platform fit: All three models share the same battery bay geometry, contact rail, and 7.5V voltage rail. The BMS expects the same handshake across the platform, so one pack covers all three radios without modification.
- Bench tested on actual hardware: We cycled this pack through transmit loads on the BPR40 dock. The BMS handled PTT current spikes without tripping, and the charger dock accepted the pack and progressed to full-charge status normally on the first insertion after a short contact wipe.
- First insertion contact check: If the charger dock shows a fault LED on first seating, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The BPR40 dock requires a clean contact surface to complete the BMS handshake before the charge cycle starts.
Why the BPR40 cuts out mid-transmission on a new Ni-MH pack
Ni-MH cells ship at partial storage voltage — typically 1.0–1.1V per cell rather than the 1.2V nominal. Under PTT transmit load, that lower starting voltage can sag enough to trigger the radio's undervoltage cutoff before the pack has been fully conditioned. The BMS reads the sag as a fault and drops the RF output or kills the transmission entirely. Running two or three full charge-discharge cycles through the dock brings cell voltage up to nominal and stabilises internal impedance. After conditioning, the cutout behaviour stops.
Bar indicator showing one fewer bar than expected on a new PMNN4071
The BPR40 uses a simple voltage-threshold bar indicator — each bar maps to a voltage band, not a fuel gauge calculation. A new pack at storage voltage sits below the top threshold, so the radio displays one bar short of full even when the pack is not depleted. This is not a capacity fault. Seat the pack in the dock, run a complete charge cycle until the dock LED goes solid green, then check the indicator again — it should read full at or above 8.4V resting voltage.