Telefunken TM 360 Cosi Replacement Battery 3.7V 1300mAh

Telefunken TM 360 Cosi — 3.7V Li-ion Replacement Battery (TM360,V2)

This 3.7V Li-ion cell delivers 1300mAh (4.81Wh) to the Telefunken TM 360 Cosi handset. It fits the TM 360 Cosi and TM360 models, restoring power to calls, messaging, and core phone functions. Dimensions are 53.90 × 43.80 × 5.40mm — confirm these against your original cell before fitting.

• TM 360 Cosi and TM360 fit: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. One cell covers both variants without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the TM360 platform. The BMS accepted charge current correctly, voltage held steady under modem load, and no thermal events occurred during the test.
• 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.

Sudden shutdown at 20–30% on the TM 360 Cosi after a cell swap

A new cell has a steeper voltage-discharge curve than an aged original. Under modem or screen load, voltage can drop sharply even when the fuel gauge still reads 20–30%. The phone's low-voltage protection triggers a hard shutdown before the percentage reaches zero. Run one full discharge-charge cycle without fast charging — this gives the coulomb counter enough data to remap the new cell's curve and stop premature cutoffs.

Phone not powering on after the replacement cell sat in storage

Li-ion cells self-discharge during storage. If the cell voltage drops below approximately 2.5V, the BMS enters a lockout state and blocks normal charge current to protect the cell. The phone will show no sign of life on a standard charger. Connect the phone to a charger and leave it undisturbed for 20–30 minutes — most BMS firmware applies a trickle recovery current at this stage. If the phone does not respond after that period, check charger output is at least 5V 500mA.