Plusfon U120e Replacement Battery 3.7V 950mAh

Plusfon U120e / 401 / 401i — 3.7V Li-ion Replacement Battery

This is a 3.7V, 950mAh (3.52Wh) lithium-ion cell for the HTC U120e, 401, and 401i smartphones. It slots into the original battery bay and connects to the same charge IC and fuel gauge circuit the phone shipped with. If your original cell swells, drains fast, or no longer holds a charge, this replaces it directly.

• U120e, 401, and 401i compatibility: These three HTC models share the same battery footprint, connector pinout, and BMS communication protocol. The cell dimensions are 53.78 × 34.05 × 4.80mm — any variance from those figures causes fit issues or BMS rejection at the charge IC level.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on HTC-class smartphone hardware and confirmed the BMS handshake completes without fault codes. Protection circuits tripped correctly at undervoltage and overcurrent thresholds.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins.

Sudden shutdown at 20–30% on the U120e after a cell swap

The HTC U120e uses a fuel gauge IC that stores a discharge curve learned from the original cell. After a cell swap, the IC still references that old curve. When real cell voltage drops below roughly 3.5V under modem or display load, the phone cuts out even though the percentage readout shows capacity remaining. This is a voltage cliff — the new cell cannot sustain the load at that state of charge. Running one full, uninterrupted discharge-to-charge cycle at standard rate allows the IC to relearn the cutoff voltage against the new cell's actual chemistry.

Phone warm near the battery compartment during first charge

A fresh cell has higher internal impedance than a cell that has completed several cycles. During the first charge, the charge IC pushes current into that higher resistance, and some energy dissipates as heat. This is normal for the first one or two cycles and typically reduces as impedance drops. If warmth persists beyond the third charge or the phone becomes hot to the touch, check that the charge IC is not forcing fast-charge mode into an uncalibrated cell — switch to a standard 5V charger until calibration completes.