BOWAY U11 Replacement Battery BP-401B 3.8V 2900mAh

BOWAY U11 — 3.8V Li-Polymer Replacement Battery (BP-401B)

This is a 3.8V, 2900mAh Li-Polymer battery for the BOWAY U11 smartphone. It replaces part number BP-401B. Fit this when the original cell no longer holds charge or the phone shuts down unexpectedly under load.

• BOWAY U11 fitment: The U11 uses a fixed voltage rail at 3.8V with a dedicated connector keyed to the BP-401B footprint. The BMS on this unit communicates charge state back to the system-on-chip — mismatched cells break that handshake and cause false low-battery shutdowns.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on U11 hardware. The BMS accepted the charge curve without tripping overcurrent protection, and the fuel gauge IC tracked state-of-charge within normal variance after the first full cycle.
• First-cycle fuel gauge reset: On first use after installation, disable fast charging and run one complete discharge-charge cycle from 100% down to auto-shutdown and back to full. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on a new cell

A fresh Li-Polymer cell has a steeper voltage cliff than an aged one. The U11's fuel gauge IC is calibrated to the original cell's discharge curve, so when the new cell's voltage drops sharply under modem or screen load, the IC reads it as a hard cutoff even though percentage still shows 20–30%. One full discharge-charge cycle forces the coulomb counter to re-anchor its low-voltage threshold to the new cell. After that cycle, the phone should track remaining charge accurately down to shutdown.

Phone won't power on after the battery sat in storage

Li-Polymer cells self-discharge in storage. If the cell drops below approximately 2.5V, the BMS enters lockout mode to prevent damage and blocks normal boot. Plug the U11 into a wall charger — not a PC USB port — and leave it for 20–30 minutes without pressing the power button. A wall adapter supplies enough trickle current to push the cell back above the 2.5V threshold and release the BMS lockout. Once the charge indicator appears on screen, the battery is accepting current normally.