About this replacement
MeiZu 16S / 16S Pro — 3.85V Li-Polymer Replacement Battery (BA971)
This is a 3500mAh (13.48Wh) Li-Polymer cell built to the BA971 specification. It fits the MeiZu 16S, 16S Pro, M973Q, and M1973 smartphones. Voltage is 3.85V nominal — matching the original cell's charge and discharge parameters.
- 16S and 16S Pro shared platform: Both phones run the same Snapdragon 855 power rail and use an identical connector pinout. The BMS handshake protocol is shared across the M973Q and M1973 variants, so one BA971 cell covers all four models without modification.
- Bench tested on actual hardware: We cycled this cell through the MeiZu charge IC and confirmed the BMS accepted the handshake on the first connection. Charge termination tripped correctly at 4.40V. Protection cutoff activated as expected under a simulated dead-short.
- Fuel gauge recalibration after swap: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC build a fresh discharge curve against the new cell before high-current charging pushes current into an uncalibrated state.
Sudden shutdown at 20–30% on the replacement cell
This is a voltage cliff — not a faulty cell. When the Snapdragon 855 fires the modem at full power or the screen peaks, the new cell briefly dips below the BMS cutoff threshold even though the coulomb counter still reads 25%. The fuel gauge IC is still calibrated to the old, worn cell's internal resistance curve. One full discharge to shutdown, then a full charge to 100% without interruption, gives the IC enough data to remap the new cell's voltage-capacity curve. After that cycle, shutdowns at partial charge typically stop.
MeiZu fast charging not accepted on the first cycle after replacement
The MeiZu charge IC runs a brief negotiation with the BMS before enabling its proprietary fast charge protocol. On a fresh cell, the BMS may report a high internal resistance figure during this handshake, and the charge IC defaults to standard 5W input as a precaution. This is expected behaviour on cycle one. Completing a full standard-rate charge cycle first resets the IC's learned resistance baseline, and fast charging typically re-enables on the next plug-in without any further steps.