Standard Horizon HX280S Replacement Battery 7.4V 1800mAh

Standard Horizon HX280S Series — 7.4V Li-ion Replacement Battery (FNB-V105Li)

This is a 7.4V, 1800mAh Li-ion replacement for the FNB-V105Li battery pack. It fits the Standard Horizon HX280S, HX280, HX280E, and HX380 handheld VHF marine radios. Same voltage, same connector, same BMS handshake protocol as the original.

• HX280S, HX280, HX280E, HX380 compatibility: These four models share the same battery bay geometry, 7.4V rail, and contact pinout. The FNB-V105Li BMS communicates directly with the radio's charge controller — swapping packs across these models works without modification.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on an HX280S dock. The BMS held stable under PTT transmit loads and tripped cleanly at low-voltage threshold without locking out the radio's charge circuit.
• Contact strip care on first dock insertion: 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 Standard Horizon charge controller requires a clean contact cycle to register the new BMS before charging begins.

Why the HX280S drops transmit power mid-call on a new FNB-V105Li

The HX280S draws a sharp current spike the moment PTT is pressed — marine VHF transmit loads hit around 1.5A. A new cell shipped at storage voltage (roughly 3.7V per cell) has higher internal impedance than a fully charged cell. That impedance causes a voltage sag under the transmit spike, and the radio's BMS interprets it as a low-voltage condition. One full charge cycle to 8.4V brings impedance down and eliminates the drop.

Bar indicator showing one fewer bar than expected after installing FNB-V105Li

The HX280S uses a simple voltage-threshold bar indicator — each bar maps to a fixed voltage band, not a charge percentage. Fresh packs ship at storage voltage, which sits in the second bar's threshold range. This is not a capacity fault. Charge the pack fully in the dock until the charge LED goes green, then power the radio on — the indicator will read correctly at full charge voltage.