Marantz FNB-V105Li 7.4V 1800mAh Li-ion Replacement Battery

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

This is a 7.4V, 1800mAh Li-ion replacement battery for the Marantz HX280S portable two-way radio. It also fits the HX280, HX280E, and HX380. The OEM part numbers are FNB-V105Li, FNB-105Li, and SBR-41Li.

• HX280S, HX280, HX280E, HX380 fit group: These four models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The 7.4V nominal voltage rail is consistent across the series, so one pack covers all four without any wiring or housing modification.
• Bench tested on actual hardware: We ran this pack through full charge and discharge cycles on the HX280S dock. The BMS responded correctly to transmit-current spikes at PTT press, held the voltage rail steady during sustained RF output, and tripped no overcurrent faults across the test sequence.
• First-insertion contact check: 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 HX280-series charger requires a clean contact cycle to complete the BMS handshake before charging begins.

Why the HX280S drops to reduced TX power mid-shift on a fresh pack

A new cell ships at storage voltage — typically 3.7–3.8V per cell, not the 4.2V full-charge peak. When the radio draws transmit current from a partially charged pack, the voltage sags further under load. The HX280S interprets that sag as a depleted pack and steps down RF output to protect the finals. A full charge cycle before the first shift eliminates this behaviour entirely.

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

The HX280-series uses simple voltage-threshold steps to drive the bar indicator — each bar corresponds to a voltage band, not a calibrated fuel reading. A new pack at storage voltage sits in the second or third threshold band, so the display shows fewer bars than the cell actually holds. Charge the pack fully in the dock until the charge LED goes green, then power on the radio — the indicator will read correctly at or above 8.3V open-circuit.