35H00141-00M AT&T Inspire 4G Replacement Battery 3.7V 1250mAh

AT&T Inspire 4G — 3.7V Li-ion Replacement Battery (35H00141-00M)

This is a 3.7V, 1250mAh Li-ion replacement battery for the AT&T HTC Inspire 4G smartphone. It slots into the same battery bay as the original and connects to the same three-contact pogo strip. Voltage and capacity match the OEM specification exactly.

• Inspire 4G battery bay fit: The Inspire 4G uses a removable battery with a fixed three-contact layout — positive, negative, and a thermistor line the charge IC uses to monitor cell temperature. This cell matches that contact arrangement and the 51.40 × 46.10 × 4.90mm bay dimensions, so the back cover seats flush without pressure on the contacts.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Inspire 4G platform. The BMS accepted the charge handshake on the first cycle, the thermistor line reported correctly, and the charge IC did not flag an over-temperature fault at full current.
• Fuel gauge recalibration on first use: After installation, run one complete discharge down to auto-shutoff, then charge uninterrupted to 100% before normal use. The Inspire 4G fuel gauge IC maps its coulomb counter to a learned discharge curve — skipping this step leaves the gauge calibrated to the old cell's curve, not the new one.

Why the Inspire 4G reports wrong battery percentage after a cell swap

The Inspire 4G uses a coulomb-counting fuel gauge IC that builds a discharge model from accumulated cycle data. When you swap the cell, the IC still holds the old cell's curve in memory — it hasn't seen the new cell's actual voltage-to-capacity relationship yet. The result is a percentage readout that doesn't match real charge state, sometimes jumping several points or reading 100% well before the cell is full. One complete discharge-to-shutoff followed by an uninterrupted charge to 4.2V lets the IC overwrite the old curve with data from the new cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity problem. Under high-current load — LTE modem transmitting or screen at full brightness — the cell voltage drops sharply at a specific state of charge, hitting the hardware undervoltage cutoff before the percentage gauge reaches zero. It happens most on new cells that haven't completed a calibration cycle, because the fuel gauge IC is reporting percentage from a curve that doesn't match the new cell. Run one full discharge cycle and charge back to 4.2V. If shutdowns continue past two cycles, check that the thermistor contact is seated fully — a floating thermistor causes the charge IC to apply conservative current limits, which accelerates apparent capacity fade.