Deviser AT400 Replacement Battery HYLB-1378 11.1V 5200mAh

Deviser AT400 / E7000A — 11.1V Li-ion Replacement Battery (HYLB-1378)

This is an 11.1V, 5200mAh Li-ion battery for the Deviser AT400 digital theodolite and E7000A surveying instrument. It powers the electronic display, angle measurement electronics, and onboard data functions. Capacity is sourced from product specification — 57.72Wh total usable energy.

• AT400 and E7000A platform fit: Both instruments share the same battery bay geometry, voltage rail, and BMS handshake protocol. The 11.1V three-cell configuration matches the power rails for the display driver and angle sensor circuits on both models.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on the AT400 platform. The BMS handled the initialisation current spike at instrument power-up without tripping, and cell balance held within 20mV across all three cells after five cycles.
• First field deployment step: After installing the battery, run a full calibration cycle through the instrument menu before leaving for site. The AT400 maps battery state during calibration — skipping this causes premature low-battery warnings during the first measurement session even with a fully charged pack.

BMS lockout after the AT400 sat unused in a carry case for months

Li-ion cells self-discharge at roughly 2–3% per month. After a long storage period, cell voltage can drop below the BMS recovery threshold — typically 2.5V per cell on this pack. When that happens, the BMS enters a protective lockout state and the instrument will not power on or accept a charge. To recover the pack, connect it to a charger that supports a low-current pre-charge or conditioning mode, which trickle-charges the cells back above the 2.5V per cell threshold before the BMS re-enables normal charge current. If the charger shows no activity after 30 minutes, the cells may have dropped below the point of BMS recovery.

AT400 display drops to zero percent and shuts down mid-session with no warning

This happens when the voltage-threshold indicator in the instrument has not recalibrated to the new cell's discharge curve. The instrument was previously reading an aged battery with a steep voltage drop near end of charge — the new cells hold voltage flatter for longer, then drop sharply, which the uncalibrated indicator reads as sudden depletion. The fix is to run two full charge-discharge cycles through the instrument's normal operation before trusting the percentage display. After two cycles, the instrument's threshold logic resets to match the new pack's curve and low-battery warnings return to accurate timing.