HTC Wildfire E2 BST01 Replacement Battery 3.85V 4000mAh

HTC Wildfire E2 — 3.85V Li-Polymer Replacement Battery (BST01)

This is a 3.85V, 4000mAh Li-Polymer cell that replaces the original BST01 battery in the HTC Wildfire E2 smartphone. It fits the Wildfire E2 only — no other HTC models share this form factor or connector. Capacity is rated at 15.4Wh, matching the original specification.

• Wildfire E2 fitment: The BST01 uses a fixed connector position and a BMS that communicates directly with the Wildfire E2 charge IC. The cell dimensions — 89.90 x 60.80 x 4.30mm — leave no clearance for a misfit. If the connector seats fully and the phone powers on, the BMS handshake is good.
• Bench tested on actual hardware: We ran the BST01 through charge and discharge cycles on the Wildfire E2 platform. The BMS held the charge IC handshake without dropping the charging session, and the fuel gauge IC accepted the new cell curve after one full cycle.
• First-cycle fast charge tip: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell discharge curve before high-current charging pushes current into an uncalibrated cell.

Why the Wildfire E2 reports wrong battery percentage after a cell swap

The Wildfire E2 uses a coulomb counter in the fuel gauge IC to track charge state. That counter was calibrated against the original cell's discharge curve — voltage versus capacity at various loads. A new cell has a slightly different curve, so the fuel gauge reads the wrong state-of-charge until it relearns it. One full discharge down to auto-shutdown, followed by a full charge to 100%, resets the learned curve. After that cycle, percentage reporting stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display draws a high current spike and the cell voltage drops below the BMS cutoff threshold — even though the fuel gauge still shows charge remaining. On a new cell before recalibration, the fuel gauge does not yet know where the voltage cliff sits. The phone cuts out because the BMS sees the instantaneous voltage drop, not the percentage on screen. Run one full discharge-recharge cycle and the fuel gauge IC will map the cutoff point correctly, typically around 3.4–3.5V under load.