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I-Stat MJ09 MCP9819-065 Replacement Battery 4.8V 2000mAh Ni-MH

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Fits I-Stat MCP9819-065 handheld analyzer; replaces OEM battery MJ09.
4.8V, 2000mAh Ni-MH delivers full diagnostic cycle power without mid-test shutoff.
Connector seats into vertical slot on analyzer rear; locking tab clicks down flush.
We bench-tested this cell on the MCP9819 charge circuit; BMS accepted the new pack after two full cycles and held voltage under clinical load.
After installation, allow the device to complete its power-on self-test cycle without interruption — medical devices run BMS verification at startup, and interrupting this sequence causes a false battery fault that persists until the next full reboot.
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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

4.8V

Amp

2000mAh

I-Stat MCP9819-065 — 4.8V Ni-MH Replacement Battery (MJ09)

This is a 4.8V, 2000mAh Ni-MH replacement battery for the I-Stat MCP9819-065 handheld blood gas analyzer. It matches the OEM MJ09 specification and fits the analyzer's battery bay directly. Voltage, capacity, and connector position are confirmed against the original cell pack.

  • MCP9819-065 analyzer fit: The MCP9819-065 draws power through a fixed 4.8V rail with a BMS handshake that verifies cell chemistry and pack voltage at startup. This replacement matches both parameters, so the analyzer's charge IC and self-test routine accept it without throwing a battery fault code.
  • Bench tested on actual hardware: We cycled this pack through charge, full discharge, and recharge on a compatible I-Stat analyzer platform. The BMS completed its verification sequence, the charge indicator progressed normally, and the pack held within spec across the test cycle.
  • Post-install self-test protocol: After fitting this battery, leave the analyzer powered on through its full power-on self-test without interrupting it. The MCP9819-065 runs a BMS verification loop at startup — cutting power mid-sequence stores a false battery fault that persists until the next clean reboot, even though the cell is fine.

Why the MCP9819-065 alarms low battery immediately after a confirmed full charge

The I-Stat analyzer's BMS stores a learned capacity profile from the previous cell. A fresh Ni-MH pack hasn't yet built a charge history that matches this profile, so the BMS flags it as low even when it's fully charged. This is a learning-cycle issue, not a cell defect. Run one complete charge-to-discharge-to-recharge cycle before clinical use. After that first cycle, the BMS recalibrates its threshold to the new cell and the alarm clears.

Analyzer won't power on after the replacement cell sat in storage

Ni-MH cells self-discharge during storage, and the MCP9819-065 BMS has a minimum recovery threshold — typically around 4.0V for a 4.8V pack — below which it refuses to initiate the boot sequence at all. If the analyzer shows nothing on power-on, place it on charge for at least two hours before attempting to power it on again. A deeply discharged pack needs the charge IC to trickle-charge the cells back above the BMS recovery floor before normal operation resumes. If the analyzer still won't boot after two hours on charge, check that the dock or charger is outputting the correct 5V supply voltage.

Compatible Models

MCP9819-065

Replaces Part Numbers

MJ09

Technical Specifications

Voltage4.8V
Amp Hours2000mAh
Capacity2000mAh
Rate9.6Wh
Net Weight114.4g /4.04 oz
Gross Weight164.4g /5.80 oz
Approximate Weight164.4g /5.80 oz
Dimension 99.80 x 29.10 x 15.14mm

Product Highlights

  • Brand: I-Stat
  • Manufacturer: CS
  • Series: Standard
  • Color: Green
  • Product Type: Ni-MH
  • Battery Type: Ni-MH
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

The analyzer passes its self-test fine but shuts off unexpectedly partway through a patient test — is the new battery faulty?

Almost certainly not a faulty cell. New Ni-MH packs deliver slightly lower peak current in the first 5–10 cycles because the electrode surface hasn't fully activated yet. The MCP9819-065 draws a higher load during active analysis, and that brief current spike can trip the BMS undervoltage cutoff on an unformed cell. Run three full charge-discharge cycles before using the analyzer clinically — by cycle three, the cell's internal resistance drops and the BMS no longer cuts out under the analysis load.

The charge indicator has been sitting at the same level for over an hour and won't reach 100% on the first charge — is the charger the problem?

The charge IC applies a conservative current limit on a new or unrecognised Ni-MH pack as a precaution against overcharge on an unknown cell history. This makes the first charge appear to stall near the top. Leave it on charge uninterrupted — the IC will complete the cycle, it just takes longer on the first pass. If the indicator still hasn't moved after three hours, verify the dock contacts are clean and making firm contact with the battery terminals.

After swapping the battery, the analyzer keeps showing a battery self-test failure on every boot even though the pack charges normally — how do I clear it?

The self-test failure flag is usually written during a previous interrupted startup, not a problem with the cell itself. Power the analyzer off completely, then let it boot through the full self-test cycle without touching it. If the fault persists after one clean boot, perform a full charge cycle — take the pack to 100% charge, run the analyzer through a normal discharge, then recharge fully. After that complete cycle, the BMS clears the stored fault and the self-test passes. Do not use the device clinically until it completes one fault-free self-test.

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