About this replacement
LG AX390 — 3.7V Li-ion Replacement Battery (LGIP-A1700E)
This is a 3.7V, 1700mAh (6.29Wh) Li-ion replacement battery for the LG AX390 mobile phone. It replaces OEM part numbers LGIP-A1700E and SBPL0081101. Fit this battery when the original cell no longer holds a usable charge or the phone shuts down unexpectedly under load.
- AX390 platform fit: The AX390 uses a single-cell 3.7V Li-ion pack with a three-contact connector tied to a basic BMS handshake. The connector pinout and physical dimensions match the LGIP-A1700E footprint, so no modification is needed to seat the replacement.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the AX390 platform. The BMS accepted the cell on first insertion, charge termination triggered correctly at 4.2V, and voltage under modem load held stable without triggering the low-voltage cutoff prematurely.
- Fuel gauge recalibration on first use: After fitting this battery, disable fast charging and run one full discharge-to-charge cycle before returning to normal use. This gives the fuel gauge IC time to map the new cell's discharge curve — skipping this step is the main cause of erratic percentage readings in the first few days.
Why the AX390 reports wrong battery percentage after a cell swap
The AX390 uses a coulomb-counter-based fuel gauge IC that builds its capacity model from previous charge and discharge cycles. When a new cell goes in, the IC still references the old degraded cell's curve. The result is a percentage readout that does not match actual remaining charge — the phone may show 40% and cut out, or show full and drop fast. One complete discharge down to automatic shutdown, followed by a full charge to 4.2V, forces the IC to rebuild its model against the new cell.
Sudden shutdown at 20–30% on the replacement cell
This is a voltage cliff problem, not a capacity problem. When the modem transmits or the screen peaks in brightness, current draw spikes and the cell voltage dips sharply. If the fuel gauge IC is still calibrated to an old weak cell, it sets cutoff thresholds too high — the phone interprets the voltage sag as empty and shuts down. The fix is the same recalibration cycle: drain the battery fully until the phone powers off on its own, then charge uninterrupted to 100%. After one cycle, the IC resets its low-voltage floor to match the new cell's actual sag behaviour.