About this replacement
Samsung Galaxy S23 Ultra — 3.88V Li-Polymer Replacement Battery (EB-BS918ABY)
This 3.88V, 4900mAh Li-Polymer cell replaces the original battery in the Samsung Galaxy S23 Ultra, covering SM-S918B, SM-S918Q, SM-S918N, and over a dozen additional regional variants. It matches the OEM voltage rail, connector pinout, and BMS communication protocol required by the S23 Ultra's power management IC. Capacity is rated at 19.01Wh.
- S23 Ultra platform compatibility: The SM-S918 series uses a shared power rail architecture across regional variants — same BMS handshake, same four-pin flex connector, same charge IC negotiation. One cell specification covers all listed variants without modification.
- Bench tested on actual hardware: We ran this cell on an SM-S918B unit and confirmed the BMS accepted the new cell without throwing fault codes. The charge IC stepped through trickle, CC, and CV phases correctly. No thermal events or handshake rejections occurred during the test cycle.
- Fuel gauge recalibration on first install: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated coulomb counter — preventing erratic percentage readings from the start.
Why the S23 Ultra shuts down suddenly at 20–30% after a cell swap
This happens because the fuel gauge IC is still referencing the discharge curve of the old, degraded cell. The new cell has a steeper, healthier voltage curve — when load spikes from the modem or display push current draw, the IC misreads available capacity and triggers a low-voltage shutdown prematurely. The fix is a full uninterrupted discharge down to automatic shutdown, followed by a full charge without interruption. After one complete cycle, the coulomb counter resets its reference curve to match the new cell and the shutdowns stop.
USB-PD fast charge not negotiating on the first cycle after replacement
On the first charge cycle after installation, some S23 Ultra units default to standard 5V/1A charging rather than accepting 25W or 45W fast charge. The charge IC holds back fast-charge negotiation until it has confirmed a minimum cell voltage and a valid BMS handshake — with a new cell at partial charge, this check sometimes fails on the first attempt. Let the phone charge to 100% on standard charge first, then disconnect and reconnect the fast charger. Subsequent sessions negotiate correctly once the charge IC has logged a baseline charge profile for the new cell.