Micronix MB-300 Replacement Battery 4.8V 4500mAh Ni-MH

Micronix MSA338 / MSA358 — 4.8V Ni-MH Replacement Battery (MB-300)

This is the MB-300 replacement battery for the Micronix MSA338 and MSA358 survey and test instruments. It runs at 4.8V with a 4500mAh (21.6Wh) Ni-MH cell pack. If your original battery no longer holds a usable charge through a field session, this is the direct swap.

• MSA338 and MSA358 compatibility: Both models share the same battery bay dimensions, connector pinout, and 4.8V supply rail. The BMS handshake is identical across the two, so one battery spec covers both without modification.
• Bench tested on actual hardware: We cycled this pack through the MSA338's probe initialisation sequence, where inrush current spikes sharply at sensor power-up. The BMS held through repeated cold-starts without tripping the protection circuit.
• First-use calibration cycle: After installing this pack, run a full calibration cycle through the instrument menu before heading into the field. The MSA338 and MSA358 map battery state during calibration — skip this step and the instrument will throw premature low-battery warnings on your first measurement session.

BMS lockout after the MSA338 sat unused in a carry case for months

Ni-MH cells self-discharge over storage, and if the pack drops below approximately 3.6V total, the BMS enters a protective sleep state. In this condition, the instrument sees no voltage on the battery rail and behaves as if no pack is installed. A standard charger may not wake the cells because its activation threshold is above what the depleted pack can present. Use a charger with a recovery or trickle-charge mode — apply 100mA to 150mA until the pack climbs above 4.0V, then resume normal charge.

Instrument shuts off mid-session during sustained sensor logging

During continuous data logging, the sensor array draws a steady load that older or degraded Ni-MH cells cannot sustain cleanly. Voltage sags under this load until it crosses the instrument's undervoltage cutoff, triggering an abrupt shutdown — even if the battery indicator showed adequate charge before the session. This is a voltage-sag failure, not a capacity failure, and it appears sooner as cells age. If shutdowns occur consistently after 20–30 minutes of active logging, check resting voltage after a full charge — it should read at or above 5.2V on a fresh pack.