About this replacement
Apple iPhone 5 — 3.8V Li-Polymer Replacement Battery (616-0611)
This is a 3.8V, 1590mAh Li-Polymer replacement battery for the Apple iPhone 5. It fits all iPhone 5 variants, including MD645LL/A and MD644LL/A. Swap it when the original cell can no longer hold charge through a normal day of use.
- iPhone 5 platform fit: All iPhone 5 variants share the same battery bay, connector pinout, and BMS handshake. The fuel gauge IC communicates over a single-wire protocol — the replacement cell carries the same authentication data as OEM part 616-0611, so iOS recognises it without a service prompt.
- Bench tested on actual hardware: We cycled this cell on an iPhone 5 board and monitored BMS cutoff behaviour across charge and discharge. The protection circuit held the correct 4.2V charge ceiling and triggered undervoltage cutoff at the expected low-cell threshold with no anomalous trips.
- Fuel gauge recalibration after install: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before drawing high current into an uncalibrated cell — skipping this step is the main cause of erratic percentage readings.
Sudden shutdown at 20–30% on the iPhone 5 after a cell swap
The iPhone 5's fuel gauge IC stores a learned discharge curve from the old, degraded cell. When a new cell is installed, the IC still references that old curve and miscalculates the actual remaining capacity. Under a sudden load spike — LTE radio switching bands or the screen at full brightness — the new cell's voltage briefly sags below the IC's cutoff threshold. The phone shuts down even though the cell has charge left. One full discharge-to-shutdown followed by a full charge-to-100% forces the coulomb counter to resync to the new cell. After that cycle, the shutdown threshold should stabilise.
Device not powering on after the replacement battery sat in storage
Li-Polymer cells in storage self-discharge over time. If the cell dropped below 2.5V per cell during transit or warehousing, the BMS locks out to prevent damage to the cell chemistry. The iPhone will show nothing on screen — not even a low-battery icon. Connect the phone to a 5W USB-A charger, not a fast charger, and leave it for 20–30 minutes without pressing any buttons. The charge IC will slowly recover the cell voltage above the BMS re-enable threshold, typically around 2.9–3.0V, at which point the phone will show the low-battery screen and begin normal charging.