EB-BSX400 Panasonic X200 Replacement Battery 3.7V 600mAh

Panasonic X200 / X400 Series — 3.7V Li-ion Replacement Battery (EB-BSX400)

This is a 3.7V, 600mAh Li-ion cell for the Panasonic X200, X400, EB-A500, and EB-X200 smartphones. It replaces OEM part numbers EB-BSX400 and EB-BSX400CN. Fit this cell when the original no longer holds a full charge or causes unexpected shutdowns.

• X200 and X400 platform compatibility: These models share the same battery bay dimensions, connector pinout, and BMS handshake protocol — one cell covers the full listed range without modification.
• Bench tested on actual hardware: We cycled this cell on the X200 platform and confirmed BMS charge acceptance from a depleted state. The protection circuit tripped correctly at the low-voltage threshold and reset cleanly on charge reconnection.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one full discharge-charge cycle at standard rate. The fuel gauge IC on these handsets calibrates its coulomb counter against the new cell's discharge curve — skipping this step causes percentage readouts to drift by 10–20% until the IC self-corrects.

Sudden shutdown at 20–30% on the X200 after a cell swap

The X200's fuel gauge IC stores a learned discharge curve from the previous cell. When a new cell is installed, the IC uses that old curve to predict remaining capacity. The new cell has a steeper voltage cliff under modem and display load than the IC expects, so the phone hits the hardware undervoltage cutoff before the software counter reaches zero. One complete discharge to automatic shutdown, followed by a full charge at standard rate, forces the IC to rebuild its curve against the new cell. After that cycle, shutdowns below 15% drop off sharply.

Phone will not power on after the replacement cell sat in storage

Li-ion cells self-discharge during storage, and if the voltage drops below approximately 2.5V per cell the BMS engages a lockout to prevent damage from deep discharge. The X200 will show nothing on screen — no charge animation, no vibration — when plugged in immediately after. Connect the phone to a wall charger rated at least 5V/1A and leave it untouched for 15–20 minutes. The BMS trickle-charges the cell from lockout up to the minimum activation voltage, at which point the phone will show the charging screen and resume normal operation.