Aeroflex AT400 11.1V Replacement Battery HYLB-1378A 5200mAh

Aeroflex AT400 — 11.1V Li-ion Replacement Battery (HYLB-1378A)

This is an 11.1V 5200mAh (57.72Wh) Li-ion battery for the Aeroflex AT400 portable test and measurement instrument. It replaces OEM part HYLB-1378A and fits directly into the AT400 battery bay. Use it for field survey work, signal testing, and extended data collection sessions where a fresh pack is the difference between finishing a job and heading back to the vehicle.

• AT400 platform fit: The AT400 draws power across a 3S Li-ion configuration at 11.1V nominal. The battery connector and BMS handshake match the instrument's power management circuit, so the AT400 reads state-of-charge correctly rather than defaulting to a flat-line estimate.
• Bench tested on actual hardware: We cycled this pack through the AT400's probe initialisation sequence, which pulls a short current spike at sensor power-up. The BMS handled the transient without tripping into protection mode, and the pack settled to steady draw under sustained logging load.
• Pre-deployment calibration cycle: After installing this pack, run a full calibration cycle through the AT400 instrument menu before heading into the field. The instrument maps battery state during calibration — skipping this step causes premature low-battery warnings during your first measurement session, even with a fully charged pack.

BMS cutoff when the AT400 powers up a probe or sensor module

At probe initialisation, the AT400 draws a short but sharp current spike as the sensor module comes online. An aged or partially discharged original pack can trigger the BMS overcurrent threshold at exactly this moment, cutting power before the instrument reaches its ready state. This replacement pack's cells are rated to handle the initialisation transient without the BMS flagging it as a fault. If you see the instrument shut off the instant a probe connects, check that the pack is above 10.5V before starting — below that threshold the BMS becomes more sensitive to spike events.

Readings drifting or data logging resetting mid-session

This symptom is distinct from a simple shutdown — the AT400 stays on but measurement values drift or the logging buffer resets unexpectedly. The cause is a brief voltage dropout under the sustained combined load of the sensor array, display backlight, and active data logging. The dropout is short enough that the processor does not fully reboot, but long enough to corrupt the active measurement state. To confirm this is the cause and not a sensor fault, check that cell voltage under load stays above 10.8V using the instrument's diagnostics menu.