Castles Saturn 1000 S1F2 Compatible Battery B26 3.7V 5200mAh

Castles Saturn 1000 S1F2 / Saturn 1000F — 3.7V Li-ion Replacement Battery (B26)

This is a 3.7V 5200mAh Li-ion replacement battery for the Castles Saturn 1000 S1F2 and Saturn 1000F payment terminals. It matches the OEM B26 part number and fits the original battery bay without modification. Capacity is 5200mAh (19.24Wh), sourced to match the original cell specification.

• Saturn 1000 S1F2 and Saturn 1000F compatibility: Both terminals share the same battery bay dimensions, connector pinout, and BMS communication protocol — one cell fits both. The BMS on each model uses the same handshake sequence, so no firmware differences affect recognition.
• Bench tested on actual hardware: We cycled this battery through full charge and discharge on the Saturn 1000 platform and monitored the BMS response at each stage. The protection circuit tripped correctly at the low-voltage cutoff threshold and recovered cleanly on reconnection to the charger.
• First deployment tip: After installing the battery, complete one full transaction cycle — including a receipt print — before taking the terminal into a live environment. The terminal maps battery capacity during normal operation and needs at least one complete power cycle to display the charge indicator accurately.

Terminal rebooting mid-transaction after battery swap

The Saturn 1000's receipt printer draws a short, sharp current spike each time it fires the print head. On a new battery that hasn't completed an initial charge cycle, the BMS can read this spike as an overcurrent event and cut power to protect the cell. This causes an immediate reboot mid-transaction, which looks like a software fault but is actually a BMS trip. The fix is straightforward: charge the replacement battery to full before first use, then complete two or three full print cycles on the bench before deploying the terminal in a live environment. This allows the BMS to calibrate its overcurrent threshold against the actual cell's internal resistance.

Terminal won't power on after sitting unused in storage

Li-ion cells self-discharge at roughly 1–2% per month in storage, and the Saturn 1000's standby draw accelerates that if the terminal was left powered on in a drawer. If the cell drops below approximately 2.5V, the BMS enters a deep-discharge lockout state and the terminal won't respond to the power button at all. Connect the terminal to its original charger and leave it undisturbed for 30–60 minutes — the charger applies a low-current recovery charge that brings the cell back above the BMS re-enable threshold. Once the charge indicator shows any activity, a normal charge cycle will restore full function. If the screen shows no response after 90 minutes on charge, the cell may be below the recovery floor and a replacement battery is needed.