About this replacement
IONYX Endy NT Series — 3.6V Ni-MH Replacement Battery (VH803821)
This 3.6V, 700mAh Ni-MH cell replaces the original battery in the Endy NT, Endo Master V2, Apex Express, and Endo Master V3, along with six additional compatible models. All units share the same voltage rail, connector pinout, and OEM part number family (VH803821 / BAT003 / BAT002). Dimensions are 44.60 × 19.50 × 19.50mm — a direct physical match to the factory cell.
- Cross-model compatibility across the Endy NT platform: The Endy NT, Endo Master V2, Apex Express, and Endo Master V3 all run the same 3.6V Ni-MH chemistry and share identical BMS handshake requirements. One cell specification covers the full platform without modification.
- Bench tested on actual hardware: We cycled this cell through charge and full-load discharge on the Endy NT platform. The BMS accepted the cell cleanly, passed its internal verification sequence, and held voltage within the expected band across the discharge curve.
- Post-installation self-test protocol: After fitting this cell, allow the device to complete its full power-on self-test without interrupting power. Medical device BMS firmware runs a verification pass at startup — cutting power mid-sequence triggers a false battery fault that persists until the next clean reboot.
Low battery alarm on the Endy NT immediately after a confirmed full charge
The Endy NT's charge monitoring firmware compares cell behaviour against stored OEM chemistry thresholds. A new Ni-MH cell delivers a slightly different charge acceptance curve than a broken-in cell, and the BMS can flag it as below threshold even when the cell is fully charged. This is a calibration gap, not a cell fault. One complete charge-discharge cycle allows the BMS to update its reference and the alarm clears. Run the device through one full cycle before clinical use.
Device will not power on after the replacement cell sat in storage
Ni-MH cells self-discharge during storage — typically losing 1–2% capacity per day at room temperature. If the cell drops below the Endy NT's BMS recovery threshold (approximately 3.0V for a 3.6V nominal cell), the protection circuit blocks power-on to prevent damage. Connect the device to its charger for a minimum 30-minute pre-charge pass before attempting to boot. Once voltage recovers above the BMS floor, the device powers on normally.