T-Mobile Affinity Li3708T42P3h553447 Compatible Battery 3.7V 800mAh

T-Mobile Affinity / N295 / Zest 2 / R250 — 3.7V Li-ion Replacement Battery (Li3708T42P3h553447)

This is a 3.7V, 800mAh Li-ion cell that replaces the original Li3708T42P3h553447 battery. It fits the T-Mobile Affinity, N295, Zest 2, and R250 handsets. Swap it in when the original cell no longer holds a charge or the phone shuts down unexpectedly under load.

• Affinity / N295 / Zest 2 / R250 compatibility: These four models share the same battery bay dimensions, 3.7V nominal voltage rail, and connector pinout — the Li3708T42P3h553447 slots into all of them without modification to the contact strip or back cover fitment.
• Bench tested on actual hardware: We ran this cell through charge and load cycles on the bench. The BMS held voltage within the expected 3.0–4.2V window and did not trigger overcurrent cutoff during a simulated screen-plus-modem draw event.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging and run one full discharge-to-charge cycle before resuming normal use. The phone's fuel gauge IC is calibrated against the old cell's discharge curve — one complete cycle lets it remap against the new cell before high-current charging begins.

Why the Affinity reports wrong battery percentage after a cell swap

The Affinity uses a coulomb-counter-based fuel gauge IC that builds its percentage model from the previous cell's charge history. When you swap in a new cell, that stored model no longer matches the actual discharge curve. The phone may show 80% and jump to 10% without warning. One full discharge cycle — draining to auto-shutdown and then charging uninterrupted to 100% — forces the IC to rewrite its reference table against the new cell's actual capacity.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display pulls a brief high-current spike and the cell's voltage drops below the BMS cutoff threshold — even though the percentage display shows charge remaining. The fuel gauge is reading state-of-charge, not instantaneous voltage under load. A fresh Li-ion cell at rest may read 3.75V but sag to 3.0V under combined modem and screen load if the IC hasn't mapped the new cell correctly. After one full calibration cycle, the percentage reading aligns closer to actual usable capacity and the premature shutdowns stop.