Pax IS057-E Replacement Battery 3.7V 1800mAh Li-ion

Pax IS057-E — 3.7V Li-ion Replacement Battery (IS057-E)

This 3.7V 1800mAh lithium-ion battery replaces the internal cell in the Pax IS057-E payment terminal. It restores power to the terminal for card processing, receipt printing, and wireless connectivity between charges. Capacity is rated at 6.66Wh, matching the original cell specification.

• Pax IS057-E platform fit: The IS057-E terminal uses a single-cell 3.7V Li-ion configuration with a battery management system that verifies cell voltage and connector polarity at boot. This cell matches that voltage rail and connector layout, so the BMS accepts it through the normal handshake sequence without throwing a hardware fault.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a payment terminal load profile — display active, wireless radio polling, and a print trigger mid-cycle. The BMS held the connection through the current spike from the receipt printer motor and did not trip to overcurrent cutoff.
• Post-installation cycle before live deployment: After fitting this battery, complete one full transaction cycle before putting the terminal into service. The IS057-E maps battery capacity during normal operation and needs at least one complete power cycle to calibrate the on-screen charge indicator correctly.

Terminal not completing PCI boot sequence after battery swap

The IS057-E runs a PCI-compliant security check during every boot, and part of that sequence includes a BMS handshake confirming the battery is within accepted voltage range. A new cell shipped in storage mode may sit below 3.5V, which can cause the terminal to stall partway through the boot sequence or restart in a loop. Connect the terminal to the charging cradle or USB-C power supply immediately after installation and allow it to charge for at least 20 minutes before attempting to power on. Once the cell reaches approximately 3.6V, the BMS handshake completes and the PCI sequence runs through normally.

Charge indicator stuck at 99% on first charge

This is normal behaviour on a new lithium-ion cell. The charge IC on the IS057-E enters a top-off phase near full capacity, reducing current to a trickle while the cell absorbs the final charge. The indicator stays at 99% during this phase because the terminal does not register 100% until the charge IC sends a termination signal, which can take 30 to 60 minutes after the display reads near-full. Leave the terminal on charge and do not interrupt the cycle. The indicator will step to 100% once the top-off phase ends and the charge IC terminates.