About this replacement
Kyocera JAX S1360 / Rally S1370 — 3.7V Li-ion Replacement Battery (SCP-55LBPS)
This is a 3.7V, 700mAh Li-ion cell that replaces the original SCP-55LBPS battery in the Kyocera JAX S1360, S1360 JAX, Rally S1370, and S1370. It fits the same 50.00 × 34.00 × 4.70mm footprint and connects to the same board contact. When the original cell degrades and the phone starts shutting down early or refusing to hold a charge, this cell restores normal function.
- JAX S1360 and Rally S1370 shared platform: Both devices run the same connector pinout, voltage rail, and charge IC, which is why they share one OEM part number. The BMS on this cell communicates on the same data line the original firmware expects — no hardware modification needed.
- Bench tested on actual hardware: We ran this cell through a full discharge-charge cycle on the S1360 board. The charge IC accepted the cell on the first connection, BMS handshake completed without fault codes, and the fuel gauge IC began tracking coulomb count from cycle one.
- Fuel gauge recalibration on first use: After installation, disable fast charging if your carrier plan or phone settings allow it, then run one full discharge-charge cycle at standard rate. The fuel gauge IC on the S1360 was calibrated to the old cell's discharge curve — a single slow cycle lets it remap against the new cell before fast-current charging is applied.
Why the JAX S1360 shuts down suddenly at 20–30% after a cell swap
The S1360's fuel gauge IC holds a learned discharge curve from the original cell. When a new cell is installed, the IC does not immediately know where the voltage cliff sits on the new cell's curve. Under modem load — during a call or data burst — the new cell's voltage drops faster than the IC expects, crossing the BMS cutoff threshold before the displayed percentage reaches zero. The phone cuts power to protect the cell, even though the gauge still shows charge remaining. One complete discharge-charge cycle at standard rate forces the coulomb counter to relearn the new cell's actual capacity endpoints.
Phone not powering on after the replacement cell sat in storage
Li-ion cells self-discharge during storage at roughly 1–2% per month, but if the cell dropped below 2.5V per cell the BMS locks out to prevent damage — the phone will show nothing when you press the power button. Connect the phone to a wall charger, not a USB port, and leave it for 15–20 minutes without pressing any buttons. Most S1360 charge ICs will trickle current into a locked-out cell at around 100mA until voltage climbs above the 2.9V re-enable threshold, after which normal charging resumes. If the screen still shows nothing after 20 minutes, switch cables and confirm the charger outputs at least 5V 1A.