About this replacement
Topwise Z91 — 7.4V Li-ion Replacement Battery (YJ455385)
This is a 7.4V, 2500mAh Li-ion replacement battery for the Topwise Z91 mobile payment terminal. It replaces OEM part number YJ455385 and fits the Z91 form factor directly. The battery slots into the terminal's rear bay and connects via the standard pogo-pin contact plate.
- Z91 platform fit: The Z91 runs a dedicated battery bay with a fixed contact layout and a BMS handshake over the data line. This cell matches that voltage rail and communicates the correct cell parameters so the terminal's charge IC does not reject it at boot.
- Bench tested on actual hardware: We cycled this cell through the Z91's full charge IC sequence, verified BMS handshake acceptance, and confirmed the terminal completed its PCI boot sequence without fault codes on the status screen.
- First transaction cycle after swap: After fitting this battery, run at least one complete transaction — card tap through receipt print — before deploying in a live environment. The Z91 maps battery capacity during normal operation and requires a full power cycle to calibrate the charge indicator correctly.
Terminal not completing PCI boot sequence after battery swap
The Z91's PCI boot sequence includes a battery validation step where the charge IC reads cell parameters from the BMS before allowing the OS to load. A new cell that has not completed its first charge-discharge cycle may sit at a resting voltage that the charge IC flags as ambiguous. The terminal stalls at the boot splash screen or cycles back to the Topwise logo repeatedly. Plug the terminal into its dock, allow a full charge to 8.35V, then power on — the boot sequence completes normally after that first charge cycle.
Battery indicator stuck at 99% through the first full charge
On a new cell, the Z91's charge IC enters top-off mode when the cell reaches approximately 8.3V, delivering a low taper current to bring it to the true full-charge threshold. During this phase the display holds at 99% rather than stepping to 100%. This is normal behaviour — the IC is not frozen, it is completing the CV stage of the charge cycle. Leave the terminal on the dock until the charge LED goes green, which signals the IC has exited top-off mode and logged the full capacity baseline for the gauge.