Dejavoo QD2 Payment Terminal Replacement Battery 7.4V 3400mAh

Dejavoo QD2 / QD4 — 7.4V Li-ion Replacement Battery

This 7.4V, 3400mAh (25.16Wh) Li-ion battery fits the Dejavoo QD2 and QD4 mobile payment terminals. Both models share the same battery bay, connector, and BMS communication protocol, so one cell covers both units. Capacity is sourced from product data — 3400mAh.

• QD2 and QD4 shared battery platform: Both terminals run the same 7.4V voltage rail, use an identical physical connector, and expect the same BMS handshake on power-up. Swapping between units requires no adapters or firmware changes.
• Bench tested on actual hardware: We ran this cell through full boot cycles on both the QD2 and QD4. The BMS handshake completed without fault codes, the charge IC entered normal top-off mode, and the terminal accepted the cell without prompting a battery error screen.
• First transaction cycle after install: Complete one full transaction — print a receipt, process a card — before deploying in a live environment. The QD2 maps battery capacity during normal operation and needs at least one complete power cycle to calibrate the charge indicator correctly.

Terminal rebooting mid-transaction after battery swap

The QD2's receipt printer draws a sharp current spike the moment it fires — often 1.5A or more above idle draw. On a new cell that hasn't completed a full charge cycle, the BMS can interpret that spike as an overcurrent event and cut power to protect the cell. This trips a hard reboot, which looks like a software crash but isn't. The fix is straightforward: charge the battery to full before first use, then run several complete transaction cycles including receipt printing. Once the BMS has logged normal load patterns, nuisance trips stop.

QD2 won't power on after sitting unused in a drawer

Li-ion cells self-discharge during storage. If the QD2 sits unused for several weeks or months, the cell can drop below the BMS recovery threshold — typically around 2.5V per cell — and the terminal will show no response at all when you press the power button. Connect the terminal to its original charger and leave it for 30–45 minutes without pressing anything. Most BMS circuits include a trickle-recovery mode that slowly brings the cell voltage back above the reinitialisation threshold. Once the charge LED activates normally, charge to full before powering on — target a full indicator before booting.