Mегафон T261L Replacement Battery 3.7V 700mAh Li-ion

Mегафон T261L — 3.7V Li-ion Replacement Battery

This is a 3.7V 700mAh Li-ion cell for the Mегафон T261L mobile phone. It slots into the original battery bay and restores power to the handset when the factory cell has degraded past usable capacity. Dimensions are 54.05 × 34.10 × 5.40mm — verify your original cell against these before ordering.

• T261L fit: The T261L uses a slim, low-capacity Li-ion cell on a 3.7V rail. This replacement matches that voltage rail and physical footprint. The BMS on the phone's charge IC expects a cell within that voltage window — a mismatched cell trips the protection circuit before the phone even powers on.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench, monitoring BMS cutoff at both ends. The cell held voltage through a full discharge without triggering premature low-voltage cutoff, and the charge IC accepted it without fault flags.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.

Why the T261L reports wrong battery percentage after a cell swap

The T261L tracks charge state using a fuel gauge IC that builds a model of the cell's discharge curve over time. When you fit a new cell, the IC is still running the old model. It will report percentages based on the previous cell's behaviour, not the new one. One full discharge down to auto-shutoff, followed by a full charge to 100%, forces the IC to rebuild its model against the actual cell. After that cycle, percentage readings stabilise.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under load — the modem or screen pulls current the cell can't sustain, and voltage collapses below the BMS cutoff threshold even though the fuel gauge still shows charge remaining. It is most visible during calls or screen-on use. The fuel gauge IC hasn't yet mapped where the voltage cliff sits on the new cell. Run two full discharge-charge cycles without interruption and the shutoffs should move to below 10%.