LeTV Max 2 LTH21A Replacement Battery 3.85V 3100mAh

LeTV Max 2 / X820 — 3.85V Li-Polymer Replacement Battery (LTH21A)

This is a 3.85V, 3100mAh (11.94Wh) Li-Polymer cell built to replace the original LTH21A battery in the LeTV Max 2 and X820 smartphones. It fits the internal battery bay directly and connects to the same flex ribbon harness. Use this when the original cell no longer holds a usable charge or the phone shuts down unexpectedly under load.

• Max 2 and X820 compatibility: Both the Max 2 and X820 share the same chassis dimensions, connector pinout, and charge IC — which is why they run the same LTH21A cell. The BMS handshake, protection circuitry, and 3.85V nominal rail are identical across both model variants.
• Bench tested on actual hardware: We ran this cell through charge-discharge cycles on the X820 platform and confirmed the BMS accepted the new cell without triggering overcurrent or overvoltage cutoff. The protection circuit held stable across draw spikes from the modem and display.
• Fuel gauge recalibration on first use: On the first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve accurately before high-current charging is applied to an uncalibrated cell.

Why the LeTV Max 2 reports wrong battery percentage after a cell swap

The fuel gauge IC on the Max 2 uses a coulomb counter that was calibrated to the original cell's discharge curve. When a new cell goes in, those reference points no longer match the actual cell chemistry. The IC keeps reading against the old curve, so the percentage shown on screen drifts from the real state of charge. One full discharge down to automatic shutdown followed by a complete charge cycle resets the counter and re-anchors the calibration to the new cell.

Sudden shutdown at 20–25% on the replacement cell

This happens when the modem, display, or both pull a current spike the cell can't sustain at low charge levels — voltage drops below the BMS cutoff threshold before the percentage reaches zero. It's a voltage-cliff problem, not a capacity problem. The fuel gauge IC hasn't yet learned where this new cell's voltage cliff sits. Run two full discharge-charge cycles without fast charging to let the coulomb counter establish the correct low-voltage floor. After calibration, the shutdown point should drop to below 5%.