Pentax Optio I 29518 Replacement Battery 7.4V 2600mAh

Pentax 29518 / 38403 / 46607 / 52030 Series — 7.4V Li-ion Replacement Battery

This 7.4V, 2600mAh Li-ion battery replaces the original pack across multiple Pentax survey and measurement instrument models, including the 29518, 38403, 46607, and 52030. It delivers consistent voltage to the instrument's processor, display, and sensor modules. Dimensions are 70.40 × 38.70 × 20.50mm — verify your bay clearance before installing.

• Cross-model compatibility: These Pentax instrument models share the same voltage rail, connector pinout, and BMS handshake protocol. One cell configuration covers the full group without modification.
• Bench tested on actual hardware: We ran this pack through instrument power-on, sensor initialisation, and sustained logging cycles. The BMS handled the current spike at probe power-up without tripping into cutoff, and held stable voltage throughout the logging session.
• Post-install calibration cycle: After fitting this battery, run a full calibration sequence through the instrument menu before field deployment. The instrument maps battery state during calibration — skipping this step causes premature low-battery warnings on the first measurement session even when the pack is fully charged.

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

Li-ion cells self-discharge slowly in storage. If the pack drops below approximately 2.5V per cell, the BMS enters a protective sleep state and blocks charge input — the instrument won't power on and the charger shows no activity. This isn't a dead battery; it's a protection circuit doing its job. Most chargers recover the pack by applying a low-current pre-charge pulse for 10–20 minutes before transitioning to full charge. If your charger has a "recovery" or "wake" mode, activate it first.

Instrument shuts down mid-measurement with the battery indicator still showing charge

This happens when sustained sensor load pulls the voltage low enough to trip the BMS undervoltage cutoff — even if the display was reading 40–50% moments before. The percentage indicator in these instruments is voltage-threshold based, not coulomb-counted, so it can look optimistic under load. The fix is to charge the pack fully before any extended field session and confirm the charger reached a termination voltage of at least 8.4V before disconnecting.