About this replacement
Onyx Healthcare MD1161 / Venus Series — 7.4V Li-ion Replacement Battery (9789OMD110)
This 7.4V, 4500mAh Li-ion battery replaces the OEM pack in the Onyx Healthcare MD1161 and Venus-123, Venus-153, and Venus-173 portable clinical devices. It matches the OEM part numbers 9789OMD110 and OPM-P05T. Capacity figures are taken directly from product data — 33.3Wh total energy.
- MD1161 and Venus-123/153/173 compatibility: All four models share the same 7.4V cell architecture, connector pinout, and BMS communication protocol. One battery SKU covers the full platform because the charge IC and thermistor circuit are identical across the lineup.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the MD1161 platform. The BMS completed its handshake without fault codes, and the charge IC accepted the full 4500mAh capacity after the first conditioning cycle.
- Power-on self-test protocol: After installing this battery, let the device complete its full startup self-test without pressing buttons or cycling power. Medical-grade BMS firmware runs a cell verification routine at boot — interrupting it logs a false battery fault that persists until the next clean reboot.
Device not completing boot sequence after battery swap
The Venus-series and MD1161 run a BMS learn cycle during the first few power-on sequences with a new cell. If the battery voltage sits below approximately 7.0V from storage self-discharge, the device may stall mid-boot or display a battery error before the OS loads. Connect the device to mains power and allow a full uninterrupted charge before attempting to power on. Once the cell reaches full charge, the boot sequence completes normally and the BMS clears the fault automatically.
Low battery alarm triggering immediately on a fully charged replacement
This happens because the BMS threshold calibration is tuned to the impedance profile of a cycled OEM cell. A brand-new cell has lower internal resistance and a slightly different discharge curve, so the fuel gauge reads pessimistically until it maps the new cell's behaviour. Run one complete charge-discharge cycle — charge to full, let the device draw the pack down through normal use, then charge again. After that cycle, the alarm threshold aligns to the new cell and the false low-battery warning stops.