About this replacement
Apple iPhone 6s Plus — 3.8V Li-Polymer Replacement Battery (616-00042)
This 3.8V, 2750mAh lithium-polymer cell replaces the original internal battery in the iPhone 6s Plus, covering models A1699, A1634, and A1690. It slots into the same footprint as the OEM unit and connects to the existing flex cable and fuel gauge IC. Capacity matches Apple's original 2750mAh specification for this handset.
- A1699, A1634, A1690 platform fit: These three variants share the same logic board layout, battery connector pinout, and BMS handshake protocol — one cell covers all three without modification or adapter cables.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a 6s Plus logic board. The BMS accepted charge from both 5W and 12W adapters, and fuel gauge communication initialised correctly across test units.
- First-cycle fuel gauge reset: After installation, run one full discharge to automatic shutdown, then charge to 100% uninterrupted before enabling fast charging. The coulomb counter in the 6s Plus needs a complete cycle against the new cell's discharge curve before it can report accurate percentages.
Sudden shutdown at 20–30% on a freshly fitted cell
A new lithium-polymer cell has a slightly different internal resistance profile than the aged cell the fuel gauge IC spent months learning. When the modem fires a high-current burst — during a call or LTE data transfer — voltage momentarily dips below the 3.0V cutoff threshold the BMS monitors. The phone reads this as a dead cell and shuts off, even though the displayed percentage still shows charge remaining. One full discharge-charge cycle recalibrates the IC's voltage-to-capacity map against the new cell, and the premature shutdowns stop.
Phone won't power on after sitting in storage for several months
Lithium-polymer cells self-discharge at roughly 2–3% per month in storage. If the cell drops below approximately 2.5V per cell, the BMS enters a protective lockout state and blocks normal charge current to prevent thermal runaway. Plugging into a standard charger does nothing visible at this voltage. Connect to a 5W Apple adapter — not a fast charger — and leave it for 30–45 minutes. The charge IC will trickle-charge at a low rate to bring the cell back above the 2.8V threshold, after which the BMS re-enables full charge current and the Apple logo appears.