Kinryo KC501A 4.8V Replacement Battery UZ73A 2000mAh Ni-MH

Kinryo KC501A / KC501B / KC502A / KC301A — 4.8V Ni-MH Replacement Battery (UZ73A)

This is a 4.8V 2000mAh Ni-MH replacement battery for the Kinryo KC501A and related surveying instruments. It fits the KC501A, KC501B, KC502A, and KC301A. The OEM part numbers are UZ73A, UZ-73A, and 4KR-950AAU.

• KC501A / KC501B / KC502A / KC301A compatibility: These models share a common 4.8V four-cell Ni-MH pack format, the same physical connector, and the same charge-termination logic. The instrument's charge circuit expects a delta-V peak consistent with Ni-MH chemistry — swapping to a different chemistry would cause incorrect termination and possible overcharge.
• Bench tested on actual hardware: We cycled this pack through the KC501A's charge-discharge sequence and confirmed the BMS accepted the pack without fault codes. The cell voltage stabilised correctly at full charge, and the instrument's charge-complete indicator triggered at the expected cutoff point.
• Post-install calibration cycle: After installing this pack, run a full calibration cycle through the instrument menu before field deployment. The KC501A maps battery state during calibration — skipping this step causes premature low-battery warnings during your first measurement session, even with a fully charged pack.

KC501A shutting down mid-measurement with a charged pack

The KC501A's sensor and display electronics draw a brief current spike at each measurement trigger — higher than the steady-state idle draw. A cell with even slight internal resistance degradation will sag below the instrument's undervoltage threshold during that spike, triggering a shutdown. A new pack at full capacity handles this surge without voltage sag. If shutdowns persist after installation, run the calibration cycle first, then attempt a measurement — the instrument recalibrates its voltage thresholds during that process.

Instrument readings resetting or drifting during a logging session

Sustained sensor load during a long logging session draws more current than short single measurements. If the pack cells are unbalanced or partially degraded, voltage drops progressively under that load and the instrument may reset mid-session or produce erratic readings toward the end of a session. This is different from a cold-start shutdown — the instrument powers on and runs fine initially, then fails under sustained draw. Fit a fresh pack and confirm each cell sits at or above 1.2V per cell (4.8V total) before beginning a logging session.