HTC e1 Replacement Battery 3.7V 1500mAh BM65100

HTC e1 / 603e Series — 3.7V Li-ion Replacement Battery (BM65100)

This is a 3.7V, 1500mAh Li-ion cell built to the BM65100 spec for HTC's e1, 603e, CSN, and HTX21UAA handsets. It fits the same connector footprint and communicates with HTC's onboard charge IC without modification. Dimensions are 60.18 × 53.30 × 5.00mm — measure your bay before ordering if you're unsure.

• e1 and 603e platform fit: These models share the same battery bay geometry, voltage rail, and BMS handshake protocol. One cell covers the whole group — the connector keying and BMS communication lines are identical across the listed variants.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on e1 hardware. The BMS accepted the cell without a fault flag, and the charge IC stepped through trickle, bulk, and termination phases cleanly.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging pushes current into an uncalibrated state.

Sudden shutdown at 20–30% on the HTC e1 after a cell swap

The e1's fuel gauge IC stores a discharge curve learned from the old cell. When a new cell goes in, that stored curve no longer matches the actual voltage-versus-capacity relationship of the replacement. Under modem or screen load, the cell voltage drops faster than the IC expects, and the phone cuts power to protect itself — even though the gauge still reads 20–30%. One full discharge and charge cycle forces the IC to relearn the curve and eliminates the premature cutoff.

HTC e1 won't power on after sitting in storage — BMS lockout

Li-ion cells that drop below roughly 2.5V trip the BMS into a protective lockout state. A phone that's been stored flat for weeks or months may not respond to a normal charger because the BMS won't allow current in from a standard charge voltage. Connect to a USB charger and leave it untouched for 20–30 minutes — the charge IC delivers a low-current trickle that brings the cell above the BMS re-enable threshold. Once the cell recovers to around 3.0V, normal charging resumes.