Avus C12 Replacement Battery 3.7V 1200mAh Li-ion MMDR 12

Avus C12 / C22 / Piano / S62 — 3.7V Li-ion Replacement Battery (MMDR 12)

This is a 3.7V, 1200mAh Li-ion cell built to fit the Avus C12 and a range of compatible Avus handsets. It replaces the OEM cell when the original no longer holds a usable charge. At 53.00 × 33.90 × 5.70mm, it matches the physical footprint of the factory battery exactly.

• C12, C22, Piano and S62 compatibility: These models share the same battery bay dimensions, connector pinout, and BMS communication protocol — which is why a single cell covers all of them. Voltage rail is 3.7V nominal across the entire range.
• Bench tested on actual hardware: We cycled this cell on a C12 unit and logged the BMS handshake, charge termination voltage, and cutoff behaviour at low state-of-charge. The protection circuit tripped cleanly at the expected low-voltage threshold with no false cutoffs under screen-on load.
• Fuel gauge recalibration on first install: After fitting, disable fast charging and run one full discharge-to-charge cycle before resuming normal use. This gives the fuel gauge IC time to map its coulomb counter against the new cell's actual discharge curve — before high-current charging pushes current into an uncalibrated cell.

Why the Avus C12 reports wrong battery percentage after a cell swap

The fuel gauge IC in the C12 builds its percentage model from repeated charge and discharge data on the original cell. Swap that cell and the IC is still referencing the old cell's impedance curve. The result is percentage readings that lag, jump, or plateau in the middle of a discharge cycle. One full drain-and-charge cycle forces the IC to rebuild its reference against the new cell, and readings stabilise from the second cycle onward.

Sudden shutdown at 20–30% remaining on a replacement cell

This is a voltage cliff, not a capacity problem. When the modem transmits or the screen peaks in brightness, current draw spikes sharply. A new cell with a slightly different internal resistance profile can drop below the BMS cutoff voltage during that spike — even when the gauge still reads 25%. The phone shuts off to protect the cell. Charge the phone to 100%, confirm the terminal voltage reads 4.18–4.20V with a multimeter at the connector, and repeat the full recalibration cycle to let the fuel gauge IC account for the new impedance profile.