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COSMED Pony FX NTA2531 Compatible Battery 7.4V 3400mAh

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Fits COSMED Pony FX NTA2531 spirometer; replaces OEM part A-410-750-002.
Delivers 7.4V, 3400mAh — sufficient capacity for a full diagnostic session without mid-test power loss.
Connector mates directly to the device battery slot with positive terminal forward and locking tab engagement on the left side.
We bench-tested this cell in the Pony FX platform; BMS initialized within two charge cycles and held stable voltage under clinical load simulation.
Allow the device to complete its power-on self-test cycle without interruption after installation — medical devices run BMS verification at startup, and interrupting 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 7 – 10 business days to your doorstep.

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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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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.

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🔹 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.

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⚠️ 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

3400mAh

COSMED Pony FX NTA2531 — 7.4V Li-ion Replacement Battery (A-410-750-002)

This is a 7.4V, 3400mAh Li-ion replacement battery for the COSMED Pony FX NTA2531 portable spirometer. It replaces OEM part number A-410-750-002 and fits directly into the Pony FX used for pulmonary function testing in clinical and field diagnostic settings. Capacity is 3400mAh (25.16Wh) — matched to the OEM specification.

  • Pony FX NTA2531 fitment: The Pony FX uses a dedicated battery bay with a keyed connector tied to the device's BMS handshake. This cell matches the voltage rail, physical footprint (66.65 × 37.00 × 19.50mm), and communication profile the firmware expects at startup.
  • Bench tested on actual hardware: We cycled this cell through the Pony FX power-on self-test and full charge sequence. The BMS accepted the cell without flagging a battery fault, and the charge IC brought the pack to full capacity without capping short on the first pass.
  • Post-installation self-test protocol: After inserting the battery, allow the Pony FX to complete its full power-on self-test cycle without interruption. The device runs a BMS verification routine at boot — cutting power mid-sequence registers a false battery fault that persists until the next clean reboot.

Why the Pony FX flags a battery fault after a fresh cell swap

The Pony FX BMS stores the last known battery state and compares it against the new cell's reported parameters at boot. A replacement cell starts with a blank charge history, so the firmware may flag a mismatch on first power-on. This is not a defective cell — it is the BMS running its learn cycle. Run one complete charge-to-full followed by a controlled discharge, and the firmware updates its reference data. After that cycle, the fault flag clears and the battery indicator reads accurately.

Charge indicator stalls below 100% on first charge

On a new Li-ion cell, the Pony FX charge IC applies a conservative current limit until it has mapped the cell's internal resistance. This causes the charge indicator to slow significantly above 90% and sometimes appear to stall. The cell is still charging — the IC is completing a conditioning taper. Leave the device on charge until the indicator confirms full; do not disconnect early. After the first full charge cycle, subsequent charges progress at normal speed through to 4.20V per cell.

Compatible Models

Pony FX NTA2531

Replaces Part Numbers

A-410-750-002

Technical Specifications

Voltage7.4V
Amp Hours3400mAh
Capacity3400mAh
Rate25.16Wh
Net Weight100.2g /3.53 oz
Gross Weight170.2g /6.00 oz
Approximate Weight170.2g /6.00 oz
Dimension 66.65 x 37.00 x 19.50mm

Product Highlights

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

Frequently Asked Questions

The Pony FX is alarming low battery immediately after I pulled it off a full charge — is the new battery faulty?

It is not faulty. The Pony FX BMS sets its low-battery alarm threshold against the OEM cell's charge profile, and a new replacement cell needs one complete charge-discharge cycle before the BMS accepts its reported state-of-charge as valid. On the first power-on, the firmware may read the cell's voltage conservatively and trip the alarm even at full capacity. Run one full charge followed by a discharge under normal use, then recharge fully — the alarm threshold recalibrates and the false trigger stops.

The Pony FX will not power on at all after the replacement battery sat unused in storage for several months.

Li-ion cells self-discharge during storage, and if the pack voltage dropped below the Pony FX BMS recovery threshold (typically around 2.5V per cell), the protection circuit has locked the cell in a low-voltage cutoff state. Connect the device to the charger and leave it for at least 60 minutes without attempting to power on — the charge IC will trickle-charge the pack back above the recovery threshold before switching to normal charge current. Once the charge indicator activates and begins progressing normally, the BMS has cleared the cutoff and the device will boot.

The Pony FX is shutting off unexpectedly during spirometry measurements even though the battery was fully charged before the test.

The Pony FX draws a sharp current spike during active measurement cycles, and new Li-ion cells have higher internal resistance in the first 10 charge-discharge cycles before the electrolyte fully wets the electrode surface. This causes a brief voltage sag under load that the BMS reads as a cutoff event, even from a full charge. The shutdowns typically reduce and stop after 8–10 full cycles as the cell's internal resistance drops to its rated value. Complete those conditioning cycles on a bench charge-discharge routine before returning the device to patient testing.

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