ZTE K90U Replacement Battery Li3990T44P6HI6A831 3.85V 9050mAh

ZTE K90U / ZPAD 10.1 — 3.85V Li-Polymer Replacement Battery (Li3990T44P6HI6A831)

This is a 3.85V, 9050mAh (34.84Wh) Li-Polymer replacement battery for the ZTE K90U and ZPAD 10.1 tablets. It replaces the original Li3990T44P6HI6A831 cell when the factory battery no longer holds a usable charge. The physical dimensions are 205.26 × 117.70 × 3.24mm — measure your existing cell before ordering if the tablet has had a prior repair.

• K90U and ZPAD 10.1 fitment: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol, which is why a single cell covers both. The fuel gauge IC communicates over a dedicated line — the connector must seat fully or the tablet will misread state of charge from the first boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a K90U unit and monitored BMS cutoff thresholds. The protection circuit tripped correctly at the low-voltage floor and accepted a full charge cycle without thermal anomaly or balancing fault.
• Fuel gauge recalibration after swap: After fitting this battery, run the tablet down to automatic shutoff — do not force-stop it — then charge uninterrupted to 100% without using the device. This single full cycle resets the fuel gauge IC against the new cell's actual capacity curve and clears the inaccurate percentage readings that almost always appear after a battery swap.

ZTE K90U shutting down at 15–25% battery remaining

This happens because the fuel gauge IC is still calibrated to the old cell's voltage curve. When the display backlight and WiFi radio draw current simultaneously, voltage sags faster than the gauge predicts — the protection circuit sees an undervoltage condition and cuts power before the reported percentage reaches zero. It is not a fault with the new cell. Run one complete discharge-to-shutoff followed by an uninterrupted charge to 100%, and the gauge recalibrates to the new cell's actual voltage floor. After that cycle the tablet should reach 5% or lower before shutdown.

Fast charging unavailable on the ZPAD 10.1 after battery replacement

USB-PD and proprietary fast-charge protocols require the charger and device to complete a successful negotiation handshake on the first accepted charge cycle after a battery swap. If the connector is not fully seated, the BMS reports an incomplete circuit and the charge IC defaults to standard 5V input as a fallback. Reseat the battery connector, ensure no flex cable is pinched, then connect the original ZTE charger — not a third-party cable — and allow the first cycle to complete without interruption. After one full accepted cycle, fast charge should re-enable automatically.