Yaesu SBR-12Li FTA-85L Replacement Battery 7.4V 2000mAh

Yaesu FTA-450L / FTA-750L Series — 7.4V Li-ion Replacement Battery (SBR-12Li / SBR-39Li)

This 7.4V, 2000mAh Li-ion pack replaces the SBR-12Li and SBR-39Li batteries in the Yaesu FTA-85L, FTA-450L, FTA-550L, and FTA-750L handheld aviation transceivers. These are VHF airband radios used for air-to-ground and interplane communication. Drop the original pack, seat this one, and the radio accepts the BMS handshake on first dock insertion.

• FTA-450L, FTA-550L, and FTA-750L shared battery rail: All four models in this lineup run the same 7.4V two-cell Li-ion architecture with an identical connector footprint and BMS handshake protocol — that is why one pack covers the full FTA series.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on the FTA-450L dock. The BMS held steady through PTT transmit spikes and stayed within the dock's charge acceptance window without triggering a fault LED.
• Aviation radio contact maintenance: If the FTA dock shows a fault LED on first insertion, wipe the gold contact strip on the battery with a dry cloth and reseat firmly. The FTA charging dock requires a clean contact cycle to complete the BMS handshake — oxidation or residue on the contacts will block it.

Why the FTA-750L drops to reduced TX power during sustained transmission

Aviation transceivers draw significantly more current during transmit than receive — the FTA-750L pulls a hard spike each time PTT is pressed. If cell impedance is high, voltage sags under that load and the radio's power management circuit steps down TX output to protect the final RF stage. This is not a radio fault — it is the BMS responding to a voltage floor. A new cell at storage charge (around 3.7V per cell) can trigger this on first use before the pack has been fully cycled up to 4.2V per cell.

Bar indicator showing one fewer bar than expected straight out of the box

Replacement packs ship at storage voltage — typically 3.7V per cell — not at full charge. The FTA series uses simple voltage-threshold bar indicators, so a pack at storage voltage will read one or two bars below full even though the cell is healthy. This is not a capacity fault. Seat the pack in the dock, complete one full charge cycle to 4.2V per cell, and the indicator will read correctly from that point forward.