Nidek KM500 Keratometer Replacement Battery 6V 2000mAh

Nidek KM500 / KM-500BPI Keratometer — 6V Ni-MH Replacement Battery (02904)

This is a 6V, 2000mAh Ni-MH replacement battery for the Nidek KM500 and KM-500BPI keratometers. These instruments measure corneal curvature and astigmatism in clinical ophthalmic examinations. The battery supplies the internal power rail during active patient use and standby periods between examinations.

• KM500 and KM-500BPI compatibility: Both models share the same 6V battery bay, connector pinout, and BMS handshake protocol. OEM part numbers 02904, B11304, and KM-500BPI all cross-reference to this cell configuration.
• Bench tested on actual hardware: We cycled this cell through a full charge-discharge sequence on the KM500 platform. The BMS accepted the cell without fault flags, and the self-test sequence completed normally on the first full charge cycle.
• Post-installation self-test protocol: After fitting this battery, allow the device to complete its full power-on self-test without interruption. The KM500 BMS runs a chemistry verification check at startup — cutting power mid-sequence locks in a false battery fault that won't clear until the next complete reboot.

Why the KM500 flags a low-battery alarm on a freshly charged replacement

The KM500 BMS was calibrated to the discharge curve of the original OEM Ni-MH cell. A new replacement cell has a slightly different internal resistance profile until it completes one or two full charge-discharge cycles. The BMS reads this mismatch as a low state-of-charge and triggers the alarm even though the cell is fully charged. Running one complete charge-discharge cycle lets the BMS recalibrate its threshold against the actual cell curve. After that cycle, the alarm clears and the battery indicator reads correctly.

KM500 not completing boot sequence after battery sat unused in storage

Ni-MH cells self-discharge at roughly 1–3% per day. A battery stored for several months can drop below the KM500's BMS recovery threshold — typically around 5.4V for a 6V pack — and the device will not boot or will freeze mid-sequence. Connect the battery to the charger for a full uninterrupted charge before attempting to power on the device. If the charge indicator stalls early, leave it on charge — the charge IC applies a slow trickle recovery below a certain voltage before switching to normal charge rate. Once the cell reaches 6.0V the BMS will re-initialise and the boot sequence will complete.