About this replacement
Apple iPhone 5 — 3.8V Li-Polymer Replacement Battery (616-0611)
This is a 3.8V, 1400mAh Li-Polymer replacement battery for the Apple iPhone 5. It fits all iPhone 5 variants including MD645LL/A, MD644LL/A, and the 64GB model. It replaces OEM part numbers 616-0611, 616-0613, 616-0610, and 616-0612.
- iPhone 5 platform fit: All iPhone 5 variants share the same 3.8V battery bay, connector pinout, and BMS handshake protocol. Any unit listed under the MD644 or MD645 series uses this exact cell format without modification.
- Bench tested on actual hardware: We cycled this cell on an iPhone 5 mainboard and confirmed the BMS initialised correctly on first boot. The fuel gauge IC accepted the new cell and began coulomb counting without triggering a low-voltage lockout.
- Fuel gauge recalibration after swap: After installation, run one full discharge to auto-shutdown and charge uninterrupted to 100% before resuming normal use. This lets the fuel gauge IC map its calibration curve against the new cell before the OS begins reading state-of-charge data.
Why the iPhone 5 reports wrong battery percentage after a cell swap
The iPhone 5 uses a coulomb counter inside the fuel gauge IC to track charge state. When you replace the cell, that counter still holds calibration data from the old, degraded battery. The IC will map its old discharge curve onto the new cell, which causes percentage readings to drift — often showing full charge then dropping suddenly. One complete discharge-charge cycle resets the calibration window and brings reported percentage back in line with actual cell voltage.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem or display draws a high instantaneous current and the cell voltage drops sharply below the BMS cutoff threshold — even though the reported percentage looks safe. On the iPhone 5, the combination of LTE radio activity and screen brightness can spike draw enough to cross that cutoff at around 3.5V. The fuel gauge IC hasn't yet learned the new cell's voltage-to-capacity curve, so it doesn't flag the approaching cliff. Run a full calibration cycle first and confirm the shutdown stops occurring before 15% reported charge.