AT&T Maven 2 Z831 Replacement Battery 3.7V 1800mAh

AT&T Maven 2 / Z831 — 3.7V Li-ion Replacement Battery

This 3.7V, 1800mAh Li-ion battery replaces the original cell in the AT&T Maven 2 and Z831 smartphones. It restores power for calls, messaging, and everyday app use. Capacity is 6.66Wh and dimensions are 72.74 × 53.41 × 4.67mm — measure your original before ordering.

• Maven 2 and Z831 compatibility: Both devices share the same battery bay dimensions, voltage rail, and connector pinout, which is why one cell covers both model numbers. The BMS handshake protocol is identical across the two variants.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Maven 2 unit, confirmed the BMS accepted the new cell without a protection trip, and verified the charge IC reached full termination voltage at 4.2V.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before it starts reporting accurate percentages to the OS.

Sudden shutdown at 20–30% on the Maven 2 after a cell swap

The Maven 2 fuel gauge IC stores a discharge model calibrated to the original cell's impedance curve. A new cell has different internal resistance, so the IC underestimates how fast voltage will drop under modem or screen load. When the phone demands current for a voice call or display wake, cell voltage sags below the protection threshold before the reported percentage hits zero. The BMS then cuts output to protect the cell, and the phone shuts off — even though the percentage still showed 20% or higher. One full discharge cycle down to automatic shutdown, followed by an uninterrupted charge to 100%, forces the coulomb counter to reset against the new cell's actual curve.

Phone shows wrong battery percentage after replacement

The fuel gauge IC on the Maven 2 uses a stored charge curve built from hundreds of cycles on the original cell. Drop in a new cell and that stored curve no longer matches actual cell chemistry, so percentage readings drift — often reading 80% when the cell is nearly flat, or jumping erratically between values. This is not a fault with the replacement cell. Run one complete cycle: discharge the phone until it powers off on its own, then charge without interruption to 100% with the screen off. After that single cycle the IC recalibrates and percentage reporting stabilises.