About this replacement
Apple iPhone 5s — 3.8V Li-Polymer Replacement Battery (616-0652)
This 3.8V, 1500mAh Li-Polymer cell replaces the original battery in the Apple iPhone 5s. It fits models A1234, A1528, A1457, and compatible variants sharing the same internal connector and BMS handshake. Voltage and capacity match OEM spec at 3.8V and 5.7Wh.
- iPhone 5s platform fit: All listed A-series variants use the same 30-pin flex connector and PMU (power management unit) communication protocol. The BMS in this cell reports charge state data that the iPhone 5s PMU expects — without that handshake, the OS throws false low-battery warnings.
- Bench tested on actual hardware: We ran this cell on an iPhone 5s logic board and confirmed the BMS negotiated correctly with the PMU on first insertion. Charge acceptance was normal from 0% through full, and the device did not trigger a shutdown during a full discharge cycle under screen-on load.
- Fuel gauge recalibration on first install: After fitting this cell, disable fast charging and run one full discharge-to-charge cycle before resuming normal use. This lets the fuel gauge IC build an accurate discharge curve against the new cell before the charge controller starts pushing higher current into an uncalibrated state.
Why the iPhone 5s reports wrong battery percentage after a cell swap
The iPhone 5s uses a coulomb counter inside the PMU that builds its charge map against the original cell's discharge curve. Swapping the cell does not reset that map automatically. Until a full discharge and recharge cycle completes, the OS reads percentage off a curve that no longer matches the new cell. One complete cycle — from near 0V through a full charge — lets the coulomb counter re-anchor its reference points to the replacement cell's actual behaviour.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage drops sharply under a high-draw load — the LTE modem or the backlight at full brightness can pull enough current to cause a brief voltage sag below the PMU's cutoff threshold, even when the reported percentage looks safe. It is a calibration problem, not a faulty cell. The fuel gauge IC is reading a stored curve that doesn't match the new cell's internal resistance profile. Run two full discharge-charge cycles without fast charging and the reported percentage will better track the actual voltage cliff.