Furukawa S944 Survey Instrument Replacement Battery 7.4V 1600mAh

FURUKAWA S218 / S218R — 7.4V Li-ion Replacement Battery (S944)

This is a 7.4V, 1600mAh Li-ion replacement battery for the FURUKAWA S218 and S218R handheld survey instruments. It matches the OEM part number S944 and fits the original battery compartment without modification. Voltage, connector, and BMS communication protocol match the factory specification.

• S218 and S218R compatibility: Both models run the same 7.4V power rail, share the same connector pinout, and use the same BMS handshake sequence. A single battery fits either unit — there is no electrical difference between the two variants that affects battery selection.
• Bench tested on actual hardware: We cycled this pack through the S218 instrument menu, including probe initialisation and a sustained sensor logging sequence. The BMS held stable through the initial current spike at probe power-up and did not trip during continuous data logging under load.
• Post-install calibration cycle: After fitting this battery, run a full calibration cycle through the instrument's menu before field deployment. The S218 maps battery state during calibration — skipping this step causes the instrument to display premature low-battery warnings on the first measurement session, even when the pack is fully charged.

BMS cutoff at probe or sensor initialisation on the S218

When the S218 powers up a connected probe or sensor module, it draws a short but sharp current spike to initialise the measurement circuit. If the battery's BMS has a low trip threshold — or if the pack voltage has sagged after partial discharge — this spike can exceed the cutoff limit and shut the instrument down immediately. This is not a fault with the instrument. It is a protection response in the battery. Fitting a fully charged pack and allowing a complete calibration cycle before connecting the probe module prevents this trip in normal field use.

S218 powers on but shuts off during USB data transfer to PC

USB data transfer adds a combined load — the instrument's processor, display, and USB controller all draw current simultaneously. On a partially discharged or aged cell, this combined draw pulls the voltage below the BMS cutoff threshold and the instrument cuts out mid-transfer, corrupting the session log. This is a voltage sag failure, not a USB fault. Charge the battery fully before any transfer session, and confirm the pack reads above 7.8V at the instrument's power indicator before connecting the USB cable.