Yaesu FNB-41 9.6V Ni-MH Replacement Battery FT-10

Yaesu FT-10 / FT-40 Series — 9.6V Ni-MH Replacement Battery (FNB-41 / FNB-42)

This is a 9.6V, 1000mAh nickel-metal hydride battery pack for the Yaesu FT-10, FT-10R, FT-40, and FT-40R handheld VHF transceivers. It cross-references OEM part numbers FNB-41 and FNB-42. Voltage and cell count match the original pack exactly.

• FT-10 and FT-40 platform fit: Both the FT-10 series and FT-40 series run an 8-cell Ni-MH stack at 9.6V nominal. They share the same battery bay dimensions, connector pinout, and charge termination logic — which is why one pack covers both lines.
• Bench tested on actual hardware: We cycled this pack through charge and transmit loads on the FT-10R. The BMS accepted charge termination correctly at peak voltage delta, and TX draw during sustained PTT did not trip an overcurrent cutoff.
• First-insertion contact check on the Yaesu charger 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 charger requires a clean contact cycle to read the pack voltage and begin the charge sequence.

Why the FT-10 cuts out mid-transmission on a fresh Ni-MH pack

Ni-MH cells ship at partial storage voltage — typically 1.0–1.1V per cell, which puts an 8-cell pack around 8.0–8.8V open circuit. The FT-10's TX stage pulls significantly more current than RX standby, and if the cell voltage is low enough, the voltage rail sags under that load and trips the radio's low-voltage cutoff. This is not a fault with the pack. Run one full charge cycle before the first transmit session and the cells will stabilise at their rated 1.2V per cell under load.

Bar indicator showing one fewer bar than expected after installing a new pack

The FT-10 uses a simple voltage-threshold bar indicator — each bar corresponds to a voltage window, not a fuel gauge reading. A new Ni-MH pack at storage voltage reads lower than a fully charged pack, so the radio displays fewer bars even though the pack is not depleted. This is not a capacity defect. Charge the pack fully and allow it to rest for 15 minutes before reinserting — open-circuit voltage should read 10.5V or above on a charged 9.6V Ni-MH pack, and the bar display will reflect that correctly.