Vertex Standard FNB-1 FT-2003 Replacement Battery 10.8V 1200mAh

Vertex Standard FT-2003 / FT-703A Series — 10.8V Ni-MH Replacement Battery (FNB-1, FNB-2)

This 10.8V, 1200mAh Ni-MH battery replaces the FNB-1, FNB-2, and FNB-2M cells used in Vertex Standard portable transceivers. It fits the FT-2003, FT-703A, FTC-5203, and FT-4073, among others. Voltage and connector format match OEM spec — no modification needed.

• FT-2003 / FT-703A platform fit: These models share the same battery bay dimensions, 10.8V rail, and connector pinout. One replacement covers the full FNB-1 and FNB-2 family. The BMS in each pack communicates via the same three-pin interface the charger dock uses to verify pack state before initiating charge.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on the FT-2003 platform. The BMS held cutoff correctly at low-cell threshold and did not trip during simulated PTT bursts at rated transmit current.
• First insertion into the dock: If the charger 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 complete the BMS handshake before charging begins — a partial contact breaks this sequence.

Why the FT-2003 cuts out mid-transmission on a freshly inserted battery

Ni-MH cells ship at storage voltage — typically 1.1–1.15V per cell, putting a 9-cell 10.8V pack around 9.9–10.35V at rest. When PTT is pressed, transmit current spikes sharply and the BMS sees a momentary voltage drop below its cutoff threshold. The radio drops the transmission or shuts off entirely — not a fault in the radio or the pack, but a predictable response to cells that haven't yet been conditioned. Running one full charge cycle before heavy use brings cell voltage up and reduces internal resistance enough to handle the transmit surge cleanly.

Bar indicator showing one fewer bar than expected after a full charge

Vertex Standard portables read battery level from voltage thresholds, not a charge counter. A new Ni-MH pack often holds a surface charge that drops slightly once the radio draws load, shifting the voltage reading down by one bar threshold. This is normal on the first one or two cycles as the cells settle. After two full charge and discharge cycles, resting voltage stabilises and the bar display will read consistently. If the display still reads low after three cycles, check that the dock reached full charge — a solid green LED, not blinking.