JDSU JD725C Replacement Battery 11.1V 7800mAh Li-ion

Viavi JDSU JD725C / JD726C — 11.1V Li-ion Replacement Battery

This 11.1V 7800mAh Li-ion battery replaces the internal pack in the JDSU JD725C and JD726C handheld optical power meters. Both instruments share the same battery bay, connector pinout, and BMS communication protocol. Capacity is 7800mAh (86.58Wh) — matched to the original specification.

• JD725C and JD726C compatibility: Both meters run on the same 11.1V three-cell configuration and use an identical BMS handshake. The connector orientation and locking tab are the same across both units, so one battery serves either instrument without modification.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on the JD725C platform. The BMS authenticated correctly, the charge indicator advanced normally, and the cell protection circuit tripped at the expected low-voltage threshold without triggering a fault code.
• First-cycle self-test on field instruments: After fitting this battery, allow the JD725C or JD726C to complete its full power-on self-test without interruption. The instrument runs a BMS verification routine at startup — cutting power mid-sequence causes a false battery fault that persists until the next clean cold boot.

Why the JD725C reports a low battery alarm immediately after a confirmed full charge

The JD725C uses a battery management IC that compares cell impedance and open-circuit voltage against a learned profile from the previous pack. A new cell with no charge history has higher impedance than a broken-in cell at the same state of charge. The meter interprets this as a partially depleted battery and raises the alarm even though the pack is fully charged. Running one complete charge-discharge cycle lets the BMS build a new impedance baseline, after which the alarm clears. After that first cycle, the alarm threshold sits correctly at approximately 10.2V under load.

JD725C will not power on after the battery has been sitting unused

Li-ion cells self-discharge at roughly 2–3% per month. If this battery sat in storage for several months before installation, the cell voltage may have dropped below the BMS recovery threshold — typically around 2.5V per cell, or 7.5V for the full pack. Below that point the BMS locks out load switching as a protection measure and the meter shows no response at all. Connect the pack to a compatible charger and hold it on charge for at least 30 minutes without attempting to power on; most BMS controllers include a trickle pre-charge path that recovers the cells to approximately 9V before re-enabling the output. Once the charge LED activates normally, proceed with a full charge cycle before use.