Motorola BPR40 Replacement Battery 7.5V 1100mAh PMNN4071

Motorola Mag One BPR40 / A8 / A6 — 7.5V Ni-MH Replacement Battery (PMNN4071)

This is a 7.5V, 1100mAh Ni-MH replacement battery for the Motorola Mag One BPR40, A8, and A6 two-way radios. It replaces OEM part numbers PMNN4071, PMNN4071A, PMNN4071AR, and PMNN4071AC. Slide it into the same battery bay, lock the latch, and the radio powers on.

• BPR40, A8, and A6 platform fit: These three models share the same battery bay dimensions, latch geometry, and contact layout. The BMS in this pack is tuned to the same voltage rail — 7.5V nominal — so the radio's protection circuit treats it the same as the original pack.
• Bench tested on actual hardware: We ran this pack through full charge and discharge cycles on a BPR40 dock. The BMS held stable under the transmit current spike when PTT was pressed repeatedly, and the charger advanced to trickle without fault.
• Contact strip prep on first insertion: If the dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The BPR40 dock requires a clean contact cycle to complete the BMS handshake before charging begins.

Why the BPR40 bar indicator reads low on a freshly inserted new pack

Ni-MH cells ship at storage voltage — typically 1.1–1.2V per cell — which sits below the radio's top bar threshold. The BPR40 reads voltage directly to set the bar count, so a new pack at storage voltage will show one or two bars even though the cells are not depleted. Run a full charge cycle in the dock before reading the indicator. After a complete charge, the voltage rises to approximately 8.4–8.6V and the indicator reflects the actual state of the pack.

Radio cuts out mid-transmission after PTT is held for several seconds

Sustained RF output draws significantly more current than standby — the BPR40's transmitter pulls a sharp current spike every time PTT is pressed, and a degraded or partially charged pack can sag below the radio's undervoltage cutoff under that load. This triggers an abrupt shutdown mid-transmission, not a gradual fade. The fix is a full charge cycle before the shift; if the cutout persists on a fully charged pack, measure the resting voltage with a multimeter — a healthy pack holds above 7.8V at rest. A pack reading below 7.4V at rest after a full charge has a cell with elevated internal impedance and needs replacing.