HTC One E1 BM65100 Replacement Battery 3.7V 2100mAh

HTC One E1 / 603e Series — 3.7V Li-ion Replacement Battery (BM65100)

This is a 3.7V, 2100mAh Li-ion replacement cell for the HTC One E1, 603e, and related CSN/HTX21UAA variants. It slots into any device originally fitted with OEM part BM65100, 35H00215-00M, or BA S930. Swap it in when your original cell no longer holds a charge or causes unexpected shutdowns.

• E1 and 603e platform fit: Both the E1 and 603e share the same 3.7V battery bay, connector pinout, and BMS handshake — that is why one cell covers this entire model group. The fuel gauge IC on both boards reads the same discharge curve from the BM65100 cell chemistry.
• Bench tested on actual hardware: We cycled this cell through a full charge-discharge sequence on an E1 unit. The BMS accepted the charge without throttling, temperature stayed within normal range, and the fuel gauge reached 100% without early cutoff.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter to the new cell's discharge curve before high-current charging begins pushing current into an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

The E1's fuel gauge IC retains the discharge curve of the old, degraded cell after a swap. When the modem or display fires a high-current draw, the new cell's actual resting voltage briefly dips below the threshold the IC expects at that state of charge. The phone interprets this as a critical low-voltage event and shuts down — even though the cell still has capacity. One full discharge-to-zero followed by a slow charge corrects this by forcing the coulomb counter to reset against the new cell's true voltage floor.

Phone reports wrong battery percentage after cell swap

The HTC One E1 uses a fuel gauge IC that learns the discharge curve of the cell it was calibrated against. A new cell has a different internal impedance profile, so the percentage reading drifts — often showing 100% too quickly or dropping sharply below 40%. This is not a faulty cell; it is the IC recalibrating. Run one full charge to 100%, then discharge the phone until it powers off on its own, then charge back to 100% without interruption. After that cycle, percentage reporting stabilises.