Senter S357 Replacement Battery 3.85V 5400mAh ST705894

Senter S357 / SL358 — 3.85V Li-ion Replacement Battery (ST705894)

This 3.85V 5400mAh Li-ion battery replaces the OEM pack in the Senter S357 and SL358 handheld surveying and testing instruments. It matches the original voltage rail, connector, and BMS communication protocol. Capacity is 5400mAh (20.79Wh), drawn directly from product specifications.

• S357 and SL358 platform fit: Both models share the same battery bay geometry, connector pinout, and BMS handshake sequence. A single pack covers both units because the voltage regulation and cell communication lines are identical across the S357 and SL358 hardware revisions.
• Bench tested on actual hardware: We cycled this pack through probe initialisation events, sustained sensor logging loads, and USB data transfer while connected to a host PC. The BMS held its cutoff thresholds and did not trip during the combined draw spikes recorded at probe power-up.
• First-use calibration on field instruments: After installing this pack, run a full calibration cycle through the instrument menu before deploying to site. The S357 maps battery state during calibration — skipping this step causes the instrument to issue premature low-battery warnings on the first measurement session.

BMS lockout after the S357 sat unused in a carry case for months

Li-ion cells self-discharge slowly in storage. If the pack voltage drops below approximately 2.5V per cell, the BMS enters a protective sleep state and blocks charging entirely. The instrument will show no charge activity and may not power on at all. To recover the pack, connect it to a charger that supports a low-current pre-charge mode — this trickle-feeds current below the BMS wake threshold until cell voltage climbs back above 3.0V per cell, at which point normal charging resumes.

Readings drifting or resetting mid-session during a logging run

Under sustained sensor load, voltage can sag briefly below the instrument's operating floor even when the displayed charge level looks healthy. The S357 interprets that voltage dropout as a fault condition and resets the active logging session to protect data integrity. This is not a faulty pack — it is the instrument responding to a momentary rail dip. Charge the battery to 100% before any session where continuous logging is required, and check that the battery contacts in the bay are clean and making full contact before deployment.