Spectra Precision PM5 Survey Replacement Battery 3.7V 7800mAh

Spectra Precision PM5 — 3.7V Li-ion Replacement Battery

This 3.7V 7800mAh (28.86Wh) Li-ion battery replaces the original pack in the Spectra Precision PM5 robotic total station. The PM5 is a precision survey instrument used for angle and distance measurement in construction and geodetic fieldwork. This battery fits that instrument directly — no other models confirmed in available data.

• PM5 power rail: The PM5 runs its servo motors, EDM module, and display from a single 3.7V Li-ion cell pack. The BMS must recognise the cell voltage profile on power-up or the instrument flags a battery fault before the first measurement. Cells here match the OEM discharge curve to clear that handshake.
• Bench tested on actual hardware: We cycled this pack through instrument power-up, servo initialisation, and sustained EDM ranging load. The BMS held cutoff thresholds within spec across all three draw phases — no spurious shutdowns on the bench.
• Post-install calibration step: After fitting this battery, run a full calibration cycle through the PM5 instrument menu before field deployment. The PM5 maps battery state during calibration. Skip this step and the instrument will throw premature low-battery warnings partway through your first measurement session.

BMS lockout after the PM5 sat unused in a carry case for months

Li-ion cells self-discharge at roughly 1–2% per month under normal storage. Leave a depleted pack in a case for several months and the cell voltage drops below the BMS recovery threshold — typically around 2.5V per cell. At that point the BMS latches into a protective lockout state and the instrument shows no response or a battery error on power-up. To recover, connect the pack to a Li-ion charger that supports a low-voltage recovery or "wake" mode and allow a slow pre-charge cycle until the cell climbs above 2.8V before normal charging resumes.

PM5 shuts down mid-measurement with no prior low-battery warning

This is almost always a voltage sag event, not a capacity failure. The EDM ranging module and servo drive pull a combined current spike at the moment of measurement that a degraded or cold cell cannot sustain without dropping below the BMS cutoff threshold. The instrument loses power before the display can register a low-battery state, so the warning never appears. Fit a fresh pack, allow the battery temperature to reach above 10°C before powering on, then confirm the open-circuit voltage reads at least 3.7V before starting a session.