Spectra Focus 35 Replacement Battery 11.1V 5200mAh

Spectra Focus 35 — 11.1V Li-ion Replacement Battery

This 11.1V 5200mAh (57.72Wh) lithium-ion battery fits the Spectra Focus 35 total station. It powers the instrument's angle measurement, EDM ranging, and onboard data logging functions in the field. No OEM part number applies to this pack — fitment is confirmed by voltage rail, physical form factor, and connector alignment.

• Focus 35 platform fit: The Focus 35 runs a single 11.1V three-cell Li-ion pack that feeds both the servo drive and the EDM module from one rail. The battery's BMS must handshake correctly with the instrument's power management circuit or the unit will refuse to boot. This pack meets that voltage and communication requirement.
• Bench tested on actual hardware: We ran this pack through cold-start initialisation, full servo slew cycles, and sustained EDM ranging sequences. The BMS held voltage above the instrument's cutoff threshold throughout sustained sensor load — no mid-sequence shutdowns were triggered.
• First-use calibration cycle: After fitting this pack, run a full calibration sequence through the Focus 35 instrument menu before field deployment. The instrument maps battery state during calibration, and skipping this step causes premature low-battery warnings during your first measurement session.

Why the Focus 35 shuts down mid-measurement with charge remaining

The Focus 35 draws from two separate loads simultaneously — the EDM laser and the servo motor — when ranging to a prism while rotating. That combined current spike can push an aged or partially discharged pack below the BMS cutoff threshold, triggering an abrupt shutdown even when the display shows 30–40% charge. A fresh pack with full cell capacity handles the combined draw without voltage sag reaching cutoff. If shutdowns persist after fitting a new pack, check that the battery contacts on the instrument are clean and making full surface contact.

Pack will not charge after the instrument sat unused in the carry case for months

Li-ion cells self-discharge during storage. If the pack drops below approximately 2.5V per cell (7.5V total), the BMS enters a protective sleep state and the charger will show no activity or immediately signal a fault. To recover the pack, place it on the charger for 15–20 minutes without interruption — some chargers apply a trickle pre-charge that brings cells back above the BMS wake threshold. If the charger shows no response after 30 minutes, the cells have discharged below recoverable voltage and the pack should be replaced.