About this replacement
Sanyo SCP-6650 / Katana II — 3.7V Li-ion Replacement Battery (SCP-26LBPS)
This is a 3.7V, 1500mAh Li-ion cell built to the SCP-26LBPS specification. It fits the Sanyo SCP-6650, SY-KA2, and Katana II handsets. The original OEM cell in these phones degrades after 300–500 charge cycles, and this replacement restores full charge capacity to the device.
- SCP-6650 and Katana II platform: Both the SCP-6650 and SY-KA2 share the same 3.7V single-cell architecture, connector pinout, and BMS handshake logic — which is why one cell number covers all three fit models. The charge IC on the mainboard communicates with the cell's protection circuit using the same thermistor line across the range.
- Bench tested on actual hardware: We ran this cell against a Katana II mainboard. The BMS accepted the charge handshake on the first cycle, the protection circuit tripped correctly at the low-voltage cutoff threshold, and the charge IC stepped down from CC to CV phase at the expected voltage point.
- Fuel gauge recalibration on first cycle: On first use after installation, run one full discharge-to-charge cycle with fast charging disabled. The SCP-6650 fuel gauge IC is calibrated to the original cell's discharge curve — a full slow cycle lets it map the new cell before it starts making capacity calculations under load.
Why the SCP-6650 reports wrong battery percentage after a cell swap
The SCP-6650 uses a coulomb-counting fuel gauge IC that builds its percentage model from the cell it first learned on — the original OEM battery. When you install a new cell, the IC still references that old discharge curve. The mismatch causes the reported percentage to read high or low against actual cell state. One complete discharge from 100% down to automatic shutoff, followed by a full uninterrupted charge, forces the IC to reset its learned curve against the new cell. After that cycle, percentage accuracy returns to normal operating tolerance.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC has not yet recalibrated and the cell voltage drops below the modem's minimum supply threshold before the OS expects it. The Katana II's baseband radio draws a surge of current during a call or data burst — on an uncalibrated cell, this surge can pull cell voltage below 3.2V momentarily, triggering the protection circuit to cut power. The phone shuts off even though the percentage display still shows charge remaining. Complete one full recalibration cycle and confirm the phone holds stable above 3.4V under load before returning it to normal use.