About this replacement
GFive A78 / A79 / A86 / I88 — 3.7V Li-ion Replacement Battery (A08)
This is a 3.7V, 1750mAh Li-ion replacement battery for the GFive A78, A79, A86, and I88 smartphones. It replaces OEM part number A08 and matches the original cell's voltage and capacity exactly. If your phone shuts down unexpectedly or no longer holds charge, this cell restores it to working condition.
- A78 / A79 / A86 / I88 shared platform: These four models run the same 3.7V battery rail, use the same physical footprint (65.00 × 44.16 × 5.20mm), and accept the same BMS handshake. One part number covers all four devices because the hardware is electrically identical at the battery interface.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on a GFive A78 unit. The BMS accepted the cell without fault codes, charge termination triggered correctly at 4.2V, and low-voltage cutoff engaged at the expected threshold.
- Fuel gauge recalibration after install: On first use after installing this cell, disable fast charging and run one complete discharge-charge cycle at standard rate. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.
Sudden shutdown at 20–30% on a new replacement cell
This happens when the fuel gauge IC is still calibrated to the old, degraded cell's voltage curve. The new cell's voltage drops more steeply under modem or screen load than the gauge expects, so the phone cuts power before the percentage reaches zero. It is not a fault in the replacement cell — it is a mismatch between the stored discharge model and the new cell's actual behaviour. Run two full discharge-charge cycles at standard charge rate and the gauge will relearn the curve.
Phone shows wrong battery percentage after cell swap
The coulomb counter inside the phone's fuel gauge IC retains data from the previous cell. After replacing the battery, the OS reads that stored data against a cell with a different internal resistance and capacity state, producing inaccurate percentage readings. Percentages may jump erratically or freeze for long periods. Let the phone discharge to automatic shutdown, then charge uninterrupted to 100% — this resets the coulomb counter baseline to the new cell.