About this replacement
Castles Saturn 1000 S1F2 / Saturn 1000F — 3.7V Li-ion Replacement Battery (B26)
This is a 3.7V 6400mAh Li-ion replacement battery for the Castles Saturn 1000 S1F2 and Saturn 1000F payment terminals. It slots into the rear battery compartment and restores full terminal operation. Part number B26 matches the OEM connector and BMS pinout for both models.
- Saturn 1000 S1F2 and Saturn 1000F compatibility: Both models share the same battery bay dimensions, 3.7V rail, and BMS communication protocol. The B26 part number covers both variants — the hardware is identical at the battery interface level.
- Bench tested on actual hardware: We cycled this cell through the Saturn 1000 boot sequence and ran back-to-back transaction simulations. The BMS handshake completed correctly on first boot, and the charge IC accepted the cell without throwing a fault code.
- First deployment tip for POS terminals: After fitting this battery, complete one full transaction cycle before putting the terminal into a live environment. The Saturn 1000 maps battery capacity during normal operation and needs at least one complete power cycle to calibrate the charge indicator correctly.
Why the Saturn 1000 reboots mid-transaction after a battery swap
The Saturn 1000's receipt printer draws a short current spike when it fires — typically enough to trip the BMS overcurrent protection on a new cell that hasn't completed its first full charge cycle. The BMS interprets this spike as a fault and cuts output, which drops the terminal mid-sale. Charge the replacement battery to 100% before first use and complete at least one transaction cycle so the BMS learns the normal load profile. After that initial calibration, the overcurrent threshold adjusts and the reboot issue resolves.
Terminal won't power on after sitting unused in a drawer
Li-ion cells self-discharge over time, and the Saturn 1000's BMS will refuse to boot if the cell voltage has dropped below approximately 3.0V — it treats this as a protection state, not a dead battery. Connect the terminal to its original charger and leave it for 20–30 minutes without pressing the power button. Most BMS circuits on this platform include a trickle-recovery path that will slowly bring the cell back above the 3.0V threshold, after which a normal boot sequence completes. If the charging LED never illuminates after 30 minutes, the original cell has likely dropped below the hard cutoff and replacement is the correct next step.