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Onyx Healthcare MD1161 Replacement Battery 7.4V 4500mAh

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From $103.99 USD $127.99
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Fits Onyx Healthcare MD1161 and Venus series portable monitors; replaces OEM part 9789OMD110 and OPM-P05T.
7.4V, 4500mAh Li-ion cell delivers sustained power for clinical monitoring devices in extended patient care shifts.
Connector seats vertically into the MD1161 battery slot with a single locking tab — orientation is keyed and cannot insert backward.
We bench-tested this cell on the Onyx charge circuit; BMS accepted the new pack on first insert with no fault codes or charge delays.
After installation, allow the device to complete its power-on self-test cycle without interruption — medical devices run BMS verification at startup, and stopping this sequence causes a false battery fault that persists until the next full reboot.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

Disclaimer

⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

7.4V

Amp

4500mAh

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.

Compatible Models

MD1161 Venus-123 Venus-153 Venus-173

Replaces Part Numbers

9789OMD110 OPM-P05T

Technical Specifications

Voltage7.4V
Amp Hours4500mAh
Capacity4500mAh
Rate33.3Wh
Net Weight205g /7.23 oz
Gross Weight355g /12.52 oz
Approximate Weight355g /12.52 oz
Dimension 126.65 x 60.30 x 21.50mm

Product Highlights

  • Brand: Onyx Healthcare
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-ion
  • Battery Type: Li-ion
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

The MD1161 shuts off unexpectedly during patient monitoring even though the battery shows charged — what's causing it?

New Li-ion cells have higher internal resistance in the first 10 charge-discharge cycles, and the MD1161's load profile during active monitoring draws enough current to trigger a voltage sag that the BMS reads as critically low. The device cuts power to protect the cell before it actually depletes. Run three to five full charge-discharge cycles before relying on this battery in a clinical setting — after conditioning, the sag drops and the BMS no longer trips at that load level.

The charge indicator on the Venus-153 won't reach 100% on the first charge — is the cell faulty?

It is not faulty. The charge IC on Venus-series devices applies a conservative current limit to new cells during the first charge, capping the accepted capacity short of the full 4500mAh until the cell's internal chemistry stabilises. Charge the device a second time immediately after the first cycle completes. The indicator will reach 100% on the second or third charge as the IC adjusts its termination voltage to the confirmed cell profile.

After the battery sat in storage, the MD1161 won't power on at all — no display, no response to the power button.

Li-ion cells self-discharge during storage, and if the pack voltage has dropped below the BMS recovery threshold — typically around 6.0V for a 7.4V nominal pack — the BMS locks out power delivery to prevent damage to the depleted cell. Connect the device to a mains charger and leave it for at least 60 minutes before pressing the power button. Most BMS firmware on this platform initiates a trickle recovery charge once the charger is detected, and the device will boot normally once the pack climbs above the recovery voltage floor.

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