EXFO FIP-425B Replacement Battery 3.7V 3600mAh Li-Polymer

EXFO FIP-425B / FIP-435B — 3.7V Li-Polymer Replacement Battery (880X268)

This 3.7V 3600mAh lithium-polymer pack replaces the internal battery in the EXFO FIP-425B and FIP-435B fiber inspection probes. These handheld probes capture end-face images of fiber connectors during network installation and maintenance work. Capacity and voltage match the original specification exactly — no modification needed to fit.

• FIP-425B and FIP-435B shared platform: Both models run on the same 3.7V single-cell architecture with a shared connector pinout and BMS handshake protocol. The pack communicates state-of-charge to the probe's onboard controller — a mismatched cell configuration causes the instrument to report incorrect charge levels or refuse to boot.
• Bench tested on actual hardware: We cycled this pack through probe power-up, autofocus trigger, and sustained image-capture sequences. The BMS held stable through the initialisation current spike that fires when the probe module first activates, and did not trip into protection mode under back-to-back capture loads.
• Post-install calibration on the FIP-425B: After fitting this pack, run a full calibration cycle through the probe's instrument menu before heading into the field. The FIP-425B maps battery state during calibration — skipping this step causes premature low-battery warnings on the first measurement session, even when the pack is fully charged.

BMS lockout after the FIP-425B sat unused in a carry case for months

Lithium-polymer cells self-discharge slowly during storage. If the pack drops below approximately 2.5V per cell, the BMS enters a deep-discharge lockout state and the probe will not power on — even when connected to a charger. The charger sees no draw and either does nothing or shows a fault indicator. To recover the pack, apply a low-current trickle charge at around 0.1C using a bench supply or a charger with a recovery mode until cell voltage climbs back above 3.0V, then switch to normal charging.

FIP-425B shuts off mid-session when transferring images to a PC over USB

USB data transfer adds a second load path on top of the probe's active display and controller — combined draw can exceed what a partially discharged cell delivers without voltage sag. When cell voltage sags past the BMS cutoff threshold under this combined load, the probe shuts off immediately, even if the battery indicator was showing 30–40% before the transfer started. The fix is to initiate USB transfers only when the pack is above 3.6V resting voltage. Charge fully before any session that involves back-to-back image capture followed by a bulk transfer.