Telefunken T90506 3.7V 1050mAh Replacement Battery Li-ion

Telefunken T90506 — 3.7V Li-ion 1050mAh Replacement Battery

This is a 3.7V Li-ion cell rated at 1050mAh (3.89Wh) for the Telefunken T90506 smartphone. It also fits the Telefunken TM600, Action Camera FHD170/5, and Srusoe Silber. No OEM part number exists for this cell — the SKU CS-HFC250SL is a warehouse identifier only.

• T90506 / TM600 / FHD170/5 platform fit: These models share the same compact cell footprint — 53.00 × 33.90 × 5.60mm — and a common 3.7V nominal voltage rail. The connector pinout and BMS handshake are consistent across this group, which is why one cell covers all listed variants.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a smartphone test rig. The BMS accepted charge from zero without entering lockout, held voltage steady under screen-on load, and tripped the protection circuit correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first cycle: After installation, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before enabling fast charging. This gives the fuel gauge IC a clean reference curve against the new cell — skipping this step is the main cause of erratic percentage readings in the first few days.

Sudden shutdown at 20–30% on the T90506 after a cell swap

This happens because the fuel gauge IC still holds the discharge curve of the old, degraded cell. When the new cell hits a voltage point the IC hasn't mapped correctly, the phone reads it as a safe percentage but the modem or display load pulls the terminal voltage below the shutdown threshold in milliseconds. The phone cuts out even though the coulomb counter says charge remains. One full uninterrupted discharge-to-shutdown cycle followed by a full charge resets the IC's reference and eliminates this in most cases.

Phone warm near the battery on the first few charges after replacement

A new cell has higher internal impedance than a cell that has been conditioned. During the first two or three charge cycles, the charge IC pushes current into that higher resistance, which generates more heat than you'd see with a run-in cell. This is normal and decreases as the cell settles. If warmth persists past the third full charge cycle, check that the charge voltage isn't being held above 4.2V — anything beyond that threshold on a 3.7V nominal cell points to a charge IC fault, not the battery.