About this replacement
Pax S58 — 7.4V Li-ion Replacement Battery (S58GPRS)
This 7.4V 1500mAh Li-ion battery replaces the OEM cell in the Pax S58 mobile payment terminal. It fits the S58 GPRS variant used by merchants for portable card transactions. Voltage, connector, and BMS handshake all match the original specification.
- S58 GPRS platform fit: The S58 GPRS shares a single battery form factor across its production run. The connector orientation, cell dimensions (73.16 × 35.00 × 35.40mm), and BMS communication protocol are consistent — this replacement slots in without modification.
- Bench tested on actual hardware: We ran the S58 through a full boot sequence, contactless and chip transaction cycles, and a receipt print burst. The BMS held voltage within spec throughout. No overcurrent trips during the printer motor draw spike.
- Post-install calibration on the S58: After fitting, complete one full transaction cycle before deploying in a live environment. The S58 maps battery capacity during normal operation and needs at least one complete power cycle to calibrate the charge indicator correctly.
Payment terminal rebooting mid-transaction after battery swap
The S58 draws a sharp current spike when the receipt printer motor engages. On a freshly installed cell, the BMS may interpret this spike as an overcurrent event and trip the protection circuit, cutting power mid-transaction. This is a calibration issue, not a faulty battery. Run two or three complete transaction cycles — including a printed receipt — to allow the BMS to register normal operating load and stop treating the printer spike as an anomaly.
S58 not completing PCI boot sequence on a new battery
The S58 runs a PCI security boot sequence at startup that requires stable voltage throughout. If the new cell hasn't completed a full charge-discharge cycle, the BMS handshake may not yet be accepted by the terminal's firmware, stalling the boot. Charge the battery to 100% before the first power-on, then allow the terminal to complete its full boot sequence uninterrupted. If the terminal still stalls, charge to 8.2V at the battery terminals and retry.