FNB-Z161 Vertex Standard VZ-D131 Replacement Battery 7.4V 1800mAh

Vertex Standard VZ-D131 / VZ-D135 — 7.4V Li-ion Replacement Battery (FNB-Z161)

This 7.4V 1800mAh Li-ion battery replaces the FNB-Z161 pack in the Vertex Standard VZ-D131 and VZ-D135 handheld transceivers. These are compact DMR portables used in security, facilities, and commercial field operations. Voltage and capacity match OEM spec exactly — no modifications needed.

• VZ-D131 and VZ-D135 compatibility: Both models run the same 7.4V power rail, share the FNB-Z161 connector footprint, and use the same BMS handshake protocol through the dock. One replacement pack covers both units in a mixed fleet.
• Bench tested on actual hardware: We cycled this pack on a VZ-D131 and monitored the BMS through repeated PTT transmit events. The overcurrent protection tripped correctly at high draw and reset cleanly — no latched lockout under normal transmit patterns.
• First insertion into the charging dock: 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 Vertex Standard dock requires a clean contact cycle to accept the new BMS handshake before charging begins.

VZ-D131 cuts out mid-transmission on a new FNB-Z161 pack

A new Li-ion cell ships at storage voltage — typically 3.6–3.7V per cell, not full charge. When the radio draws transmit current at storage voltage, the BMS can interpret the voltage sag as an undervoltage event and cut the output. The fix is straightforward: charge the pack fully before the first transmission-heavy shift. One full charge cycle brings the cells to 4.2V each, giving the BMS enough headroom to handle the transmit spike without tripping.

Bar indicator shows one fewer bar than expected after charging

The VZ-D131 uses a voltage-threshold bar indicator — each bar corresponds to a voltage band, not a percentage calculated by a chip. A new pack that hasn't completed a full charge cycle will sit just below the top threshold and show one bar fewer than a fully charged OEM pack. This is not a capacity defect. Run a full charge until the dock green LED holds steady, then check the indicator — it should read at the expected level once cells reach 8.4V across the pack.