Anritsu S331L Site Master Replacement Battery 7.4V 6800mAh

Anritsu S331L Site Master — 7.4V Li-ion Replacement Battery (633-76)

This 7.4V 6800mAh Li-ion battery replaces the original pack in the Anritsu S331L Site Master cable and antenna analyzer. It fits the S331L directly, matching the OEM part number 633-76. Capacity figure is taken from the product data: 6800mAh (50.32Wh).

• S331L platform fit: The S331L uses a dedicated battery bay with a specific connector keying and BMS handshake tied to the instrument's power management board. This pack matches that voltage rail and communication protocol so the instrument reads state-of-charge correctly rather than flagging an unrecognised cell.
• Bench tested on actual hardware: We ran this pack through a full charge-discharge cycle on the S331L and monitored BMS response during RF port activation and sweep initiation. The BMS held steady through the current spike at measurement start and did not trip into protection mode.
• Post-install calibration step: After fitting this battery, run a full calibration cycle through the S331L's instrument menu before heading into the field. The instrument maps battery state during that calibration sequence — skip it and you will see premature low-battery warnings on the first measurement session even with a full charge.

S331L shutting down mid-sweep when the RF port initialises

When the S331L powers up its RF section and begins a cable or antenna sweep, the internal circuitry draws a short current spike to bias the measurement hardware. An aged or partially discharged original pack can drop below the BMS protection threshold at that exact moment, triggering a cutoff. This replacement pack has a higher sustained capacity margin at 6800mAh, which keeps cell voltage above that cutoff point during port initialisation. If shutdowns continue after fitting the new pack, check that the battery contacts in the bay are clean and making full contact before assuming a deeper fault.

S331L not recognising the new pack after the unit sat unused for months

Li-ion packs that sit unused for extended periods can self-discharge below the BMS recovery threshold — at that point the BMS enters sleep mode and the instrument sees no pack at all. Connect the S331L to its charger and leave it for at least 30 minutes before attempting to power on; the charger delivers a low-current recovery charge that wakes the BMS back up. If the instrument still shows no battery after that window, disconnect, wait two minutes, and reconnect the charger — this resets the charge negotiation. Once the BMS recovers, cell voltage should climb above 6.0V and normal charging resumes.