About this replacement
Standard Horizon HX290 — 7.4V Li-ion Replacement Battery (FNB-110Li)
This is a 7.4V, 1140mAh Li-ion battery for the Standard Horizon HX290 portable VHF marine radio. It replaces OEM part FNB-110Li and fits both the HX290 and HX 290 model designations. The HX290 is a handheld marine radio, so this battery covers on-water communication in routine and emergency conditions.
- HX290 platform fit: The HX290 uses a 7.4V two-cell Li-ion pack with a specific connector and BMS handshake tied to Standard Horizon's charging dock. This replacement matches that voltage rail and connector geometry, so the dock recognises the pack and initiates the charge cycle correctly.
- Bench tested on actual hardware: We ran this pack through the Standard Horizon dock and monitored BMS response during simulated PTT transmit loads. The BMS held the voltage rail stable through repeated key-up events without triggering an overcurrent cutoff.
- Saltwater contact precaution: If the radio has been used in spray or submersion conditions, dry the battery contacts with a clean cloth before reinserting. Salt residue on the gold contact strip can cause a contact resistance fault that the dock reads as a low-voltage or bad-pack condition.
Why the HX290 cuts out mid-transmission on a freshly installed battery
When a new Li-ion pack ships from storage, its cells typically sit at 3.6–3.7V per cell — below the voltage the HX290's BMS expects under TX load. PTT draws a sharp current spike to drive the RF output stage. If the cell voltage sags under that spike, the BMS interprets it as a fault and cuts output power or drops the transmission entirely. This is not a defective battery. Run one full charge cycle through the dock before using the radio in the field, and the cells will hold the voltage headroom the TX surge needs.
Bar indicator reads one fewer bar than expected after inserting a new FNB-110Li
The HX290 uses a simple voltage-threshold bar indicator — it reads pack voltage and maps it to bars with no fuel gauge chip involved. A new cell at storage voltage often reads one bar low compared to a fully charged original. This is not a capacity fault. Place the pack in the dock, allow a full charge to completion, and the indicator will reflect the correct charge state. After a full charge cycle, expect the indicator to read full at approximately 8.4V across the pack.