About this replacement
Motorola BPR40 / Mag One A8 Series — 7.4V Li-ion Replacement Battery (PMNN4534A)
This is a 7.4V, 3400mAh Li-ion replacement battery for the Motorola BPR40, Mag One A8, Mag One A8D, and Mag One A8i two-way radios. It replaces OEM part number PMNN4534A. The cell matches the original voltage rail and connector footprint used across the Mag One platform.
- BPR40 and Mag One A8 platform fit: All four models — BPR40, A8, A8D, A8i — share the same battery bay geometry, gold contact strip, and 7.4V BMS handshake protocol. One pack covers the full series without modification.
- Bench tested on actual hardware: We cycled this pack through transmit loads on the BPR40 platform. The BMS held stable through sustained PTT bursts and did not trip the overcurrent threshold under normal push-to-talk draw.
- First-insertion contact check: If the charger dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The Mag One dock requires a clean contact cycle to complete the BMS handshake before charging begins.
Why the BPR40 cuts out mid-transmission on a freshly inserted pack
New cells ship at storage voltage — typically 3.6–3.7V per cell, not full charge. When you key up immediately after inserting a new pack, the transmit current spike can pull the cell voltage below the BMS undervoltage threshold for a split second, triggering a protective cutout. This is not a faulty battery. Run the pack through one full charge cycle before field use, and the cells will hold the voltage rail through PTT spikes without dropping out.
Bar indicator showing one fewer bar than expected on a new PMNN4534A
The Mag One platform reads battery level against fixed voltage thresholds — it does not recalibrate for new cells. A new pack at storage voltage will display one or two bars instead of full because the resting cell voltage sits below the top threshold. Charge the pack fully before reading the indicator. After a complete charge, the open-circuit voltage should sit at approximately 8.3–8.4V and the radio will display a full bar reading.