Viavi 5KR-CH JDSU EST-120 Replacement Battery 6V 4500mAh

Viavi JDSU EST-120 / EST-125 / EDT-135 — 6V Ni-MH Replacement Battery (5KR-CH)

This is a 6V 4500mAh Ni-MH replacement battery for the Viavi JDSU EST-120, EST-125, and EDT-135 OTDRs. It slots directly into the battery compartment and matches the original 5KR-CH specification. All three instruments share the same voltage rail and pack form factor, so one part number covers the full group.

• EST-120, EST-125, and EDT-135 compatibility: These three OTDR models run from the same 6V bus and use the same physical pack housing with identical connector orientation. The BMS handshake is passive on this chemistry — no authentication chip to negotiate, so the instrument reads voltage directly from the cells.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on a programmable load and confirmed the 5-cell Ni-MH stack holds stable output through the mid-discharge plateau. The BMS protection circuit tripped correctly at the low-voltage cutoff without latching — the instrument recovered cleanly on reconnect.
• Post-install calibration on the EST-120: After fitting the new pack, run a full calibration cycle through the OTDR's instrument menu before heading into the field. The EST-120 maps battery state during calibration. Skip this step and the low-battery warning can trigger early on the first measurement session, even with a fully charged pack.

EST-120 BMS lockout after the pack sat unused in a carry case for months

Ni-MH cells self-discharge continuously. A pack stored for three to six months can drop below the BMS recovery threshold — typically under 4.5V for a 5-cell stack. When the instrument sees this voltage, it refuses to power on, and placing the pack on the charger may show no charge activity at all. The fix is a trickle pre-charge: use a standalone Ni-MH charger set to a low current (around 100mA) for 30–60 minutes to bring the pack above 5V, then transfer to the standard charger to complete the cycle.

OTDR readings reset or freeze mid-logging session with no warning

During a sustained OTDR logging session, the laser source and DSP draw current simultaneously. On a partially discharged Ni-MH pack, this combined load can pull cell voltage below the instrument's operating floor for a fraction of a second — long enough to trigger a reset. This is not a firmware fault. It is a voltage sag caused by the pack's rising internal resistance as cells age. If resets are happening consistently at the same point in a test sequence, check resting voltage before the next session — a healthy 6V Ni-MH pack should read at least 6.8V immediately after a full charge.