About this replacement
MeiZu V8 Pro — 3.85V Li-Polymer Replacement Battery (BA813)
The BA813 is a 3.85V, 3000mAh (11.55Wh) Li-Polymer cell for the MeiZu V8 Pro, V8 Pro Dual SIM, V8 Pro Dual SIM TD-LTE, and M813Q. It fits directly behind the display assembly and connects to the charge IC and fuel gauge IC on the main board. Swap it when the original cell no longer holds voltage under screen or modem load.
- V8 Pro and M813Q platform compatibility: All four fit models share the same 70.00 × 61.00 × 4.07mm footprint, the same BA813 connector pinout, and the same BMS handshake with the MeiZu charge IC — so the same cell works across the entire group without modification.
- Bench tested on actual hardware: We cycled the BA813 through full charge and discharge on the V8 Pro board. The BMS held cutoff correctly at both ends, and the fuel gauge IC accepted the new cell without throwing a fault code.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.
Sudden shutdown at 20–30% on the replacement cell
A new Li-Polymer cell has a steeper voltage cliff than a worn one. When the modem transmits or the screen peaks in brightness, current draw spikes and cell voltage drops sharply — enough to trip the BMS undervoltage cutoff even though the gauge still shows 20–30%. The fuel gauge IC is still running the old cell's coulomb-count model, so it reports capacity that no longer matches actual voltage. One full slow discharge followed by a full charge resets the coulomb counter and moves the reported percentage back in line with real cell voltage.
USB fast charge not accepted on the first cycle after replacement
MeiZu's charge IC negotiates fast charge protocol only after it confirms the BMS is in a ready state. On a freshly installed cell, the BMS starts in a conservative mode and may not acknowledge the fast charge handshake on cycle one. If the phone charges slowly or falls back to 5W on the first plug-in, that is expected behaviour. Complete one full standard-rate charge, disconnect, and reconnect — the charge IC will re-negotiate and fast charge should resume at that point.