Panasonic EB-BSX500 Smartphone Replacement Battery 3.7V 720mAh

Panasonic EB-A200 / EB-X500 Series — 3.7V Li-ion Replacement Battery (EB-BSX500)

This is a 3.7V, 720mAh Li-ion replacement cell for the Panasonic EB-A200, EB-X100, and EB-X500 smartphones. It matches the OEM part number EB-BSX500 and installs directly into the original battery bay. Voltage and capacity figures come from the product data — 2.66Wh total energy.

• EB-A200 / EB-X100 / EB-X500 platform fit: These three models share the same battery bay dimensions, connector pinout, and BMS handshake protocol, which is why a single cell covers all three. The charge IC on each device reads the same thermistor resistance range, so the BMS communicates correctly without any adaptation.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the EB-X500 platform. The BMS accepted the cell on first insertion, raised no fault codes, and the charge IC stepped through trickle, constant-current, and constant-voltage phases without interruption.
• 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 against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the EB-A200 after a cell swap

The EB-A200's modem and display draw a combined load spike that can exceed 1A in bursts. When the fuel gauge IC is still calibrated to the old cell's discharge curve, it misreads the new cell's actual state of charge. The new cell hits its low-voltage cutoff — typically around 3.0V under load — while the gauge still reads 20–30% remaining. One full discharge-charge cycle with no interruption resets the coulomb counter and eliminates the mismatch.

Device not powering on after the replacement cell sat in storage

Li-ion cells self-discharge during storage. If the cell voltage drops below approximately 2.5V, the BMS enters lockout mode and blocks normal charging to prevent thermal runaway on a deeply discharged cell. The phone will show no response to the charger and no boot screen. Connect to a 5V USB charger and leave it untouched for 20–30 minutes — the charge IC applies a trickle current below BMS lockout threshold, recovers the cell voltage above 2.9V, and normal charging resumes automatically.