Swisscom Comfort VS1 Replacement Battery 3.7V 750mAh

Swisscom Comfort VS1 / VS2 — 3.7V Li-ion Replacement Battery

This 3.7V, 750mAh Li-ion cell replaces the original battery in the Swisscom Comfort VS1 and Comfort VS2 mobile phones. It matches the stock voltage rail and physical footprint — 53.80 × 33.70 × 5.80mm — so it seats correctly in both handsets. Capacity is 2.78Wh, identical to the factory specification.

• VS1 and VS2 shared platform: Both models run the same battery bay dimensions and 3.7V supply rail. The connector pinout and BMS handshake are identical across both, so one cell services either handset without modification.
• Bench tested on actual hardware: We cycled this cell through charge and full load discharge on the VS1 platform. The BMS accepted charge current without error flags and held voltage above the low-battery cutoff threshold through the complete discharge arc.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging if your charger supports it, then run one complete discharge down to automatic shutdown before recharging fully. The VS1 fuel gauge IC recalibrates its coulomb counter against the new cell's actual discharge curve during that first cycle — skipping it causes the percentage readout to drift early.

Sudden shutdown at 20–30% on the Comfort VS1 after a cell swap

This is a voltage cliff issue, not a capacity fault. When the modem fires during a call or the screen peaks brightness, current draw spikes sharply. A freshly installed cell with an uncalibrated fuel gauge IC can show 25% remaining while actual cell voltage has already dropped below the BMS cutoff threshold — typically 3.0V under load on this class of Li-ion cell. The phone interprets that voltage drop as a hard low-battery event and shuts down to protect the cell. One full discharge-to-shutdown and full recharge cycle lets the coulomb counter map the real voltage curve of the new cell and eliminate these early cutoffs.

Battery percentage jumping erratically on the VS1 after replacement

The VS1's fuel gauge IC stores a discharge curve model calibrated to the old, degraded cell. When a new cell goes in, the stored model no longer matches actual cell behaviour — so the reported percentage lurches as the IC tries to reconcile measured voltage against a curve that no longer applies. This is not a fault with the replacement cell. Charge the phone to 100%, use it until it shuts off automatically on low battery, then charge back to 100% uninterrupted. After that single full cycle, the IC recalibrates its reference points against the new cell and the percentage display stabilises.