About this replacement
Apple iPhone 8 — 3.82V Li-Polymer Replacement Battery (616-00357)
This is a 3.82V, 1820mAh Li-Polymer cell for the Apple iPhone 8. It fits models A1863, MQ7H2ZP/A, MQ6K2LL/A and other iPhone 8 variants sharing OEM part numbers 616-00357 and 616-00358. Capacity matches the original Apple specification at 6.95Wh.
- iPhone 8 model compatibility: All iPhone 8 variants listed share the same PCB layout, connector pinout, and BMS handshake protocol. The fuel gauge IC communicates over a single-wire authentication line — this cell carries the correct authentication data to pass that handshake without triggering a service warning in iOS Settings.
- Bench tested on actual hardware: We ran this cell on an iPhone 8 main board, monitoring charge IC behaviour through a full cycle. The BMS accepted charge current without fault flags, and the coulomb counter tracked state-of-charge correctly from 100% down to the low-voltage cutoff threshold.
- Fuel gauge recalibration on first use: After installation, disable fast charging and run one complete discharge-to-charge cycle at standard 5W. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated counter — preventing erratic percentage readings from the first day.
Sudden shutdown at 20–30% on a freshly installed iPhone 8 cell
The iPhone 8 modem and display together can pull over 2A during peak load. A new cell with an uncalibrated fuel gauge IC may have its voltage floor set to the old cell's discharge curve. When load spikes, the cell voltage dips past the BMS cutoff threshold even though the displayed percentage reads mid-range. The phone shuts down not because charge is gone, but because the BMS trips on a momentary voltage sag the counter didn't anticipate. One full discharge-charge cycle at standard current recalibrates the coulomb counter and eliminates this behaviour.
iOS battery percentage jumping erratically after replacement
Erratic percentage jumps — five to ten points in seconds — happen when the fuel gauge IC is still using the discharge curve stored for the original cell. The coulomb counter loses accuracy as the new cell's impedance profile diverges from that stored curve. This is not a faulty cell; it is a calibration state. Perform one uninterrupted discharge down to automatic shutdown, then charge to 100% without interruption — after that cycle, percentage reporting stabilises.