About this replacement
Sanyo SCP-4920 / RL4920 — 3.7V Li-ion Replacement Battery
This is a 3.7V, 1700mAh Li-ion replacement battery for the Sanyo SCP-4920 and RL4920 smartphones. It slots into the original battery bay and connects to the same three-contact terminal. Capacity is rated at 6.29Wh, matching the original cell specification.
- SCP-4920 and RL4920 compatibility: Both models share the same battery bay dimensions, terminal layout, and 3.7V nominal voltage rail. The BMS handshake uses the same three-pin thermistor line, so the charge IC reads cell temperature correctly on either device.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the SCP-4920 platform. The BMS held the 4.2V charge cutoff accurately and the thermistor line reported correctly throughout — no false overtemp flags triggered during testing.
- First-cycle fuel gauge reset: On first use after installation, run one complete discharge down to auto-shutoff, then charge uninterrupted to 100%. This gives the fuel gauge IC one full reference cycle against the new cell's actual discharge curve before the OS starts reporting percentage.
Why the SCP-4920 reports wrong battery percentage after a cell swap
The SCP-4920 uses a fuel gauge IC that builds its capacity model from previous charge cycles. When you install a new cell, that stored model still references the old, degraded cell's discharge curve. The IC maps voltage to percentage incorrectly until it recalibrates. One full discharge-to-shutoff followed by a full uninterrupted charge corrects the coulomb counter and aligns the percentage display to the new cell's actual capacity.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem or display draws a high current spike and the cell voltage drops sharply below the BMS protection threshold — even though the percentage looks fine. It is a voltage-cliff failure: the fuel gauge shows 25% but the cell cannot sustain voltage under load. The fix is to complete one full calibration cycle so the IC learns where the actual voltage cliff sits on this cell. After calibration, the phone will shut down closer to 5–10% rather than cutting out mid-use at 25%.