FirstData FD-400 Replacement Battery 7.4V 1800mAh Li-ion

FirstData FD-400 Series — 7.4V Li-ion Replacement Battery (FD400)

This 7.4V, 1800mAh Li-ion battery replaces the factory pack in the FirstData FD-400 payment terminal family. It fits the FD-400, FD-400Ti, FD-400Gt, and FD-410, among other variants in the same series. Voltage and connector match OEM spec — the terminal's charge controller sees no difference from the original pack.

• FD-400 series compatibility: The FD-400, FD-400Ti, FD-400Gt, and FD-410 share the same battery bay, connector pinout, and BMS communication protocol. One pack covers all these variants because the power rail and handshake logic are identical across the lineup.
• Bench tested on actual hardware: We ran this pack through full boot, transaction processing, and receipt print cycles on the FD-400 platform. The BMS accepted the cell without fault codes, and the charge IC entered normal CC/CV charging without triggering a reject state.
• First deployment cycle: After installing the battery, complete at least one full transaction cycle — including a receipt print — before deploying the terminal in a live environment. The terminal maps pack capacity during real operation and needs one complete power cycle to report the charge indicator accurately.

Terminal rebooting mid-transaction after battery swap

The FD-400's receipt printer draws a short, sharp current spike each time it fires — often 1.5A or more above baseline. On a new cell that hasn't completed a conditioning cycle, the BMS can interpret this spike as an overcurrent event and cut power to protect the cell. The result looks like a random reboot, but it happens consistently at the point the printer engages. Run the terminal through several complete transaction-and-print cycles before live use; the BMS recalibrates its trip threshold as it maps the cell's actual internal resistance.

FD-400 not powering on after sitting unused in a drawer

Li-ion cells self-discharge at roughly 1–2% per month, and the FD-400's standby draw accelerates this when the terminal is left powered but idle. If the cell drops below approximately 2.5V per cell (5.0V pack), the BMS locks out discharge to prevent damage and the terminal shows no signs of life. Plug the terminal into its dock charger and leave it for at least 30–45 minutes before attempting to power on — the charge IC needs time to trickle the cell above the BMS recovery threshold before normal charging begins. Once the pack reads above 6.0V, the BMS unlocks and the terminal boots normally.