MaxCom MM135 Replacement Battery 3.7V 900mAh Li-ion

MaxCom MM135 / MM134 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 900mAh Li-ion cell for the MaxCom MM135 and MM134 mobile phones. It replaces the original battery when capacity fade makes the phone unreliable through a normal day. Dimensions are 53.00 × 34.00 × 4.30mm — confirm these against your existing cell before ordering.

• MM135 and MM134 compatibility: Both models share the same battery bay dimensions, voltage rail, and connector pinout, so one cell covers both. Swapping between them requires no modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the MM135 platform. The BMS accepted charge current normally, and the protection circuit tripped correctly at the low-voltage cutoff threshold with no anomalies.
• Fuel gauge recalibration after swap: After fitting this cell, run one complete discharge down to auto-shutdown, then charge to 100% uninterrupted. This lets the phone's fuel gauge IC map its readings to the new cell's discharge curve before normal use begins.

Why the MM135 shuts down suddenly at 20–30% after a cell swap

The MM135 fuel gauge IC stores a discharge model calibrated to the old cell's internal resistance profile. A new cell has a different voltage-versus-capacity curve, so the gauge reads 25% when the actual cell voltage is already close to the BMS cutoff threshold. Under the load of an active call or screen-on use, voltage dips briefly below the cutoff and the phone shuts off. One full discharge-to-shutdown cycle followed by an uninterrupted charge to 100% forces the coulomb counter to resync against the new cell, resolving the early shutdown behaviour.

Phone shows incorrect battery percentage after replacement

The fuel gauge IC on the MM135 uses a stored charge curve from the previous cell — when the cell is swapped, that curve no longer matches reality and percentage readings become unreliable. You may see the indicator jump from 60% to 20% without significant use, or the phone refuse to turn on despite the gauge showing charge remaining. Drain the phone fully until it powers off on its own, then charge in a single session to 100% without interruption. After that first complete cycle, gauge accuracy returns to normal.