About this replacement
Pax X5 / X3S — 3.8V Li-Polymer Replacement Battery (PC-M116)
This is a 3.8V, 3900mAh Li-Polymer replacement battery for the Pax X5 and X3S portable payment terminals. It matches the original PC-M116 specification and fits the physical battery bay directly. Voltage and capacity are confirmed against product data — 3900mAh, 14.82Wh.
- X5 and X3S platform fit: Both terminals share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The X5 and X3S draw from the same 3.8V Li-Polymer cell architecture, so one replacement covers both devices without any hardware modification.
- Bench tested on actual hardware: We cycled this cell through the Pax BMS initialisation sequence — the charge IC accepted the new cell, the BMS handshake completed without fault codes, and the capacity register updated correctly after the first full charge cycle.
- First deployment tip for POS terminals: After fitting this battery, run one complete transaction cycle — card read through receipt print — before putting the terminal into live service. The terminal maps cell capacity during normal operation, and this single cycle lets the charge indicator calibrate correctly.
Receipt printer current spike triggering BMS cutoff mid-transaction
The Pax X5's thermal receipt printer pulls a sharp current spike the moment it starts printing. On a degraded or newly installed battery where the BMS protection threshold is sensitive, this spike can trip the overcurrent cutoff and reboot the terminal mid-sale. A new cell with full capacity handles the combined display, wireless, and printer draw without hitting that threshold. If reboots happen only at the point of receipt printing, the battery is the first component to replace — not the printer module.
Terminal stuck at 99% charge indicator after first install
A new Li-Polymer cell arrives partially charged, and the Pax charge IC enters top-off mode when it detects a cell already near full voltage — typically above 4.1V. In this mode, the indicator sits at 99% for an extended period while the IC trickle-charges the last few millivolts. This is normal charge controller behaviour, not a faulty battery. Leave the terminal on charge until the indicator clears to 100%, which confirms the charge IC has exited top-off mode and the cell is fully seated in the capacity register.