Vertex Standard D281 FNB-Z182 Compatible Battery 7.4V 1800mAh

Vertex Standard D281 / VX-D281 — 7.4V Li-ion Replacement Battery (FNB-Z182)

This is a 7.4V, 1800mAh Li-ion replacement battery for the Vertex Standard D281 and VX-D281 two-way radios. It replaces OEM part numbers FNB-Z182 and FNB-Z182ZI. The battery slots into the same housing footprint as the original and uses the same contact layout.

• D281 and VX-D281 platform fit: Both model variants share the same battery bay dimensions, contact pin arrangement, and BMS handshake protocol — one pack covers both. The 7.4V nominal rail matches what the radio's power management circuit expects at startup and during transmit.
• Bench tested on actual hardware: We cycled this pack on a D281 unit and logged the BMS response through PTT key-up events. The overcurrent protection triggered correctly at the transmit current spike and reset without faulting the radio's power circuit.
• First insertion into the charger dock: If the dock LED holds on amber or blinks fault on first seating, remove the battery, wipe the gold contact strip with a dry cloth, and reseat firmly. The Vertex Standard dock requires a clean contact cycle to complete the BMS handshake before it will begin charging.

Why the D281 drops to reduced TX power mid-shift on a new pack

New Li-ion cells ship at storage voltage — typically 3.6–3.7V per cell — not at full charge. The D281 monitors the battery voltage rail continuously and steps down transmit power when voltage falls below its internal threshold. A pack that starts at storage voltage will hit that threshold earlier in the shift than a fully charged one. Fully charge the battery in the dock before the first use to bring both cells to 4.2V and avoid this voltage sag mid-transmission.

Bar indicator showing one fewer bar than expected after fitting the FNB-Z182

The D281 reads battery level using voltage-threshold steps, not a dedicated fuel gauge chip. A new pack at storage voltage will register one or two bars even though the cell capacity is intact. This is a voltage reading, not a capacity fault. Charge the battery fully — the dock LED will go green — then reinsert into the radio and the bar indicator will reflect the actual state of charge correctly.