Anritsu 633-76 S331L Compatible Battery 7.4V 5200mAh

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

This 7.4V 5200mAh Li-ion battery replaces the OEM pack in the Anritsu S331L Site Master cable and antenna analyzer. It fits the S331L directly and matches the original connector, voltage rail, and BMS communication protocol. Capacity is sourced from the product specification — 38.48Wh total energy.

• S331L platform fit: The S331L uses a dedicated battery bay with a multi-pin connector that carries both power and BMS data to the instrument's power management IC. This replacement matches that pinout. Swapping to a pack with the wrong BMS register layout causes the S331L to flag a battery fault on startup even if voltage is correct.
• Bench tested on actual hardware: We ran this pack through the S331L's power-on sequence, including the RF module initialisation and port 1 stimulus sweep. The BMS handled the inrush current at RF subsystem startup without tripping, and the instrument accepted the pack without a battery error flag.
• First deployment after installation: After fitting the new pack, run a full calibration cycle through the S331L's calibration menu before heading to site. The instrument maps battery state during that sequence, and skipping it causes premature low-battery warnings to appear during your first measurement session even when the pack is near full charge.

BMS cutoff when the S331L initialises its RF port stimulus

At power-on, the S331L runs a self-test that activates the RF stimulus source and internal signal path simultaneously. This creates a brief but sharp current spike that can exceed the over-current threshold on a replacement pack with an undersized BMS. The result is an immediate shutdown that looks like a dead battery but is actually a protection trip. This pack's BMS is rated to handle that initialisation load without latching off, which is what we confirmed during bench testing.

S331L not recognising the pack after it sat unused in a carry case

Li-ion cells in storage self-discharge over weeks. If the pack voltage drops below approximately 2.5V per cell — around 5.0V total for a 2S pack — the BMS enters a deep sleep state and stops responding to the instrument's handshake. The S331L then shows no battery detected or refuses to power on. To recover, connect the pack to a charger that supports 0V recovery or pre-charge mode and hold it there until the BMS re-initialises — typically once the pack climbs above 6.0V.