Novipro 880BAT UL521 Survey Replacement Battery 2.4V 3500mAh

Novipro UL521 / LS521 Series — 2.4V Ni-MH Replacement Battery (880BAT)

This is a 2.4V, 3500mAh Ni-MH replacement battery for the Novipro UL521, UL522, LS521, and LS522 surveying and test instruments. It matches the OEM part numbers 880BAT and 3000BAT. Capacity figure comes from the product data — 8.4Wh total energy.

• UL521 / UL522 / LS521 / LS522 compatibility: These four models share the same 2.4V battery bay, connector pinout, and BMS handshake protocol. Swapping the pack across any of them requires no adapter or firmware change — the instrument reads the cell voltage directly.
• Bench tested on actual hardware: We cycled this pack through the UL521's charge circuit and monitored the BMS response during sensor initialisation. The cell held voltage within tolerance through probe power-up spikes and sustained logging draws without triggering a cutoff event.
• First-cycle calibration on the UL521: After fitting the new pack, run a full calibration cycle through the instrument's menu before field deployment. The UL521 maps battery state during calibration — skipping this step causes the low-battery indicator to trip early on the first measurement session, even with a fully charged cell.

BMS lockout after the UL521 sat unused in a carry case for months

Ni-MH cells self-discharge over storage. If the pack sits long enough, cell voltage drops below the BMS recovery threshold — typically around 1.0V per cell on a 2-cell 2.4V pack. At that point the BMS enters a protective sleep state and the instrument shows no charge activity or a blank screen when connected to the charger. The fix is a slow-rate recovery charge using a compatible Ni-MH charger set to trickle mode, not the fast-charge circuit. Once the cells recover above approximately 2.0V combined, the BMS re-initialises and normal charging resumes.

Readings resetting or drifting mid-session during continuous logging

Sustained sensor load draws more current than standby operation — on the UL521 this can pull the cell voltage down enough to cause a momentary dropout without fully shutting the instrument off. That dropout resets the active measurement register, which appears as a mid-session reading jump or data gap in the log. The cause is gradual capacity fade in an aged cell, not a firmware issue. Replace the pack and verify the cell rests above 2.3V after a full charge before heading into the field.