About this replacement
Sharp PV-BL31 — 3.7V Li-ion Replacement Battery (PV-BL31)
This is a 3.7V, 3000mAh (11.1Wh) Li-ion cell that replaces the original Sharp PV-BL31 battery. It fits Sharp mobile phones that use the PV-BL31 battery. Swap it in when your original cell no longer holds charge or the phone shuts down unexpectedly during normal use.
- PV-BL31 platform fit: Sharp devices in this series share the same voltage rail and connector pinout. The BMS handshake on this cell matches the charge IC the phone expects, so charging initialises without fault codes.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on compatible Sharp hardware. The BMS held cutoff within spec at both the low-voltage floor and the 4.2V charge ceiling — no thermal events, no mid-cycle disconnects.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter to the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.
Sudden shutdown at 20–30% on the replacement cell
A new cell has a slightly different discharge curve than the one the fuel gauge IC learned from the old battery. When the phone's modem fires or the screen peaks brightness, current draw spikes and the cell voltage drops faster than the gauge predicts. The phone's low-voltage protection triggers a hard shutdown even though the reported percentage still reads 20–30%. One full discharge-to-cutoff cycle followed by a full charge lets the coulomb counter recalibrate to the new cell. After that cycle, the percentage reading and the actual shutdown point should align.
Phone warm near the battery during the first few charges
A new cell arrives with higher internal impedance than a broken-in cell. The charge IC on the phone pushes current into that resistance, and some of that energy converts to heat rather than stored charge. This is normal for the first two or three cycles and fades as the cell's impedance settles. If the phone stays warm well past the third full charge cycle, check that the charge port and cable are not adding contact resistance — measure charge current with a USB meter and confirm it drops below 50mA at full charge termination.