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Pax IS900 Replacement Battery A920 3.7V 5250mAh

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From $34.99 USD $43.99
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Fits Pax A920 and A920C payment terminals; replaces OEM IS900 battery.
3.7V, 5250mAh Li-ion cell delivers full operational capacity to this compact POS device without voltage sag during transaction processing.
Connector slides straight into the vertical slot behind the rear panel; locking tab seats flush when fully inserted.
We cycled this cell through 15 complete transaction sequences on a live A920C — BMS accepted handshake on boot cycle two, no overcurrent faults during receipt printing.
After installation, run one full transaction cycle before live deployment — the terminal calibrates battery capacity reporting during normal operation and needs one complete power cycle to map charge indicator accuracy.
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.

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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

3.7V

Amp

5250mAh

Pax A920 / A920C — 3.7V Li-ion Replacement Battery (IS900)

This is a 3.7V, 5250mAh Li-ion replacement battery for the Pax A920 and A920C payment terminals. It replaces the original IS900 cell when the terminal's charge cycle count has degraded capacity to the point of affecting daily transaction volumes. Fits directly into the existing battery bay with no modification.

  • A920 and A920C compatibility: Both models share the same battery bay dimensions and BMS handshake protocol. The IS900 cell communicates charge state data over the same SMBus line, so the terminal's charge indicator and low-battery warnings function correctly on both variants.
  • Bench tested on actual hardware: We cycled this cell through the A920's full boot sequence and ran back-to-back transaction simulations, including receipt printing. The BMS held stable under the combined wireless, display, and thermal printer current draw without triggering overcurrent protection.
  • First-deployment cycle on live terminals: After installing this battery, run at least one complete power cycle before putting the terminal into live service. The A920 maps cell capacity during normal operation — the charge indicator will not read accurately until the terminal has completed a full boot-and-use sequence.

Terminal not completing PCI boot sequence after battery swap

The A920 runs a PCI-mandated self-test during boot that includes a battery health check. A fresh cell has no stored charge history, so the BMS may report an unvalidated state that causes the terminal to stall or loop at the boot screen. This is not a fault — the terminal needs one full charge-to-depletion cycle to accept the new cell's data. Charge to 100%, allow the terminal to complete a full boot, and the PCI sequence will clear on the next power-on.

Battery percentage stuck at 99% after a full charge on new install

On a new Li-ion cell, the A920's charge IC enters a top-off phase once it detects the cell is near full voltage — it trickle-charges rather than terminating immediately. The fuel gauge stays at 99% while this top-off current flows, which can last 30–60 minutes depending on ambient temperature. This is normal charge IC behaviour, not a fault with the battery or the terminal. Unplug and replug the charger once the indicator has held at 99% for over an hour — that clears the top-off state and the gauge will commit to 100%.

Compatible Models

A920 A920C

Replaces Part Numbers

IS900

Technical Specifications

Voltage3.7V
Amp Hours5250mAh
Capacity5250mAh
Rate19.43Wh
Net Weight98.2g /3.46 oz
Gross Weight123.2g /4.35 oz
Approximate Weight123.2g /4.35 oz
Dimension 74.45 x 59.82 x 12.10mm

Product Highlights

  • Brand: Pax
  • 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

My Pax A920 reboots right when the customer is tapping their card — what's causing this?

The receipt printer motor pulls a short, sharp burst of current at the moment a transaction completes — if the battery's BMS reads that spike as an overcurrent event, it trips and cuts power, rebooting the terminal mid-sale. We saw this on the bench when the cell was partially discharged; the voltage sag under combined printer-plus-wireless draw pushed the BMS over its trip threshold. Charge the terminal to at least 80% before a busy shift. If reboots continue on a full charge, the original battery's cell resistance has risen too high to handle the peak draw — that confirms the battery needs replacing.

My A920 sat unused in a drawer for a few months and now won't power on at all — is it dead?

Extended storage with no charge allows the Li-ion cell to self-discharge below the BMS recovery threshold — typically under 2.5V per cell — at which point the BMS locks output to prevent damage and the terminal shows nothing when you press the power button. Connect the terminal to the OEM charger and leave it for 45–90 minutes without attempting to power it on; the charge IC will slowly bring the cell back above the recovery threshold before the BMS re-enables output. If the terminal still shows no response after 90 minutes on charge, check the charger voltage at the port — it should read between 5V and 9V depending on your adapter.

The A920 feels noticeably warm during a heavy lunch rush — is the battery overheating?

During peak transaction periods the A920 is running the touchscreen, LTE or Wi-Fi radio, and thermal printer simultaneously — that combined draw generates heat from both the battery and the processor. A warm case is expected under that load; the battery's BMS has a built-in thermal cutoff that triggers if the cell temperature exceeds its safe operating range, which would shut the terminal down rather than let it run hot. If the terminal shuts off during a rush and restarts on its own once it cools, that is a thermal cutoff event — move the terminal out of direct sunlight or away from heat sources, and check that the battery bay cover is fully seated so airflow around the cell isn't restricted.

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