Smiths Capnocheck II Replacement Battery 7.4V 3400mAh
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Smiths Capnocheck II Replacement Battery 7.4V 3400mAh - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
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
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
⚠️ 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.
Smiths Capnocheck II Replacement Battery 7.4V 3400mAh - is backordered and will ship as soon as it is back in stock.
Voltage
7.4V
Amp
3400mAh
Smiths Capnocheck II Capnograph — 7.4V Li-ion Replacement Battery (8408)
This is a 7.4V, 3400mAh Li-ion replacement battery for the Smiths Capnocheck II Capnograph and Oximeter. It matches the OEM part number 8408 and fits the original battery bay without modification. Voltage and cell chemistry match the device's power management requirements exactly.
- Capnocheck II and Oximeter platform fit: Both the Capnograph and Oximeter variants use the same 7.4V battery bay, connector pinout, and BMS handshake protocol — a single cell design covers both units.
- Bench tested on actual hardware: We ran the battery through the Capnocheck II power-on sequence and confirmed the BMS completed its cell verification pass without triggering a fault. The charge IC accepted a full cycle from flat without interruption.
- Post-swap self-test cycle: After fitting this battery, let the device run its full power-on self-test without pressing any keys or cycling power. The Capnocheck II's BMS runs a cell verification at startup — interrupting it logs a battery fault that persists until the next clean reboot.
Why the Capnocheck II flags a battery fault after a confirmed full charge
The Capnocheck II's BMS holds voltage thresholds calibrated to an aged OEM cell's charge curve. A fresh Li-ion cell charges to a slightly higher open-circuit voltage, and the BMS can read this as out-of-spec on the first cycle. Running one complete charge-discharge cycle lets the BMS re-map the cell's internal resistance and capacity profile. After that conditioning cycle, the fault clears and the charge indicator reports accurately.
Device won't power on after battery sat in storage
Li-ion cells self-discharge over storage time. If a cell drops below roughly 2.5V per cell — around 5.0V total for a 2S pack — the Capnocheck II's BMS enters deep-discharge lockout and blocks the power-on sequence entirely. Placing the device on charge for at least 30 minutes lets the charge IC apply a low-current pre-charge recovery pulse that brings the cell back above the BMS recovery threshold. Once the pack reaches approximately 6.0V, normal charging resumes and the device powers on cleanly.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: Smiths
- 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 Capnocheck II is showing a low battery alarm right after I put in a freshly charged replacement — what's going on?
A new cell's charge curve doesn't match the voltage signature the BMS was calibrated against on the original cell, so it triggers the low battery threshold even when the pack is full. Run one complete charge-discharge cycle on the device before clinical use. After that cycle the BMS re-maps the cell and the alarm clears. Confirm the pack reads above 8.0V on the device's battery status screen before the second charge.
The Capnocheck II powers on but shuts off mid-session — the battery was showing adequate charge before it happened.
The Capnocheck II's CO2 sampling pump draws a short high-current pulse each breath cycle. In the first 10 cycles on a new cell, internal resistance is higher than it will settle to, and that pulse can cause a momentary voltage sag that trips the BMS low-voltage cutoff. This resolves as the cell conditions over the first several use cycles. Until it stabilises, avoid running the device at maximum sampling rate — drop to the standard sampling interval until the cell has completed at least five full charge cycles.
The charge indicator on the Capnocheck II stopped at around 85% and hasn't moved for two hours — is the battery faulty?
The charge IC applies a conservative current limit on the first charge of a new cell, which can stall the final constant-voltage topping phase and make the indicator appear frozen. This is normal behaviour — leave it on charge for a further 60–90 minutes without removing it. If the indicator still hasn't reached full after that period, remove the battery, refit it firmly to reset the charge IC handshake, and restart the charge cycle from the device powered off.
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