T-Mobile E110 Zest Replacement Battery 3.7V 800mAh

T-Mobile E110 Zest — 3.7V Li-ion Replacement Battery (Li3710T42P3h553457)

This is a 3.7V, 800mAh Li-ion cell that fits the T-Mobile E110 Zest compact smartphone. It matches the OEM part number Li3710T42P3h553457 and drops into the same battery bay without modification. Capacity is 800mAh (2.96Wh), identical to the original specification.

• E110 Zest platform fit: The E110 and Zest share the same battery bay geometry, connector pinout, and BMS handshake protocol — one cell covers all three model designations listed by T-Mobile.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the E110 platform. The BMS accepted the new cell without error flags, and the charge IC completed a full charge cycle to 4.2V termination without thermal cutoff.
• Fuel gauge recalibration on first use: On first installation, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before enabling fast charging. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the E110 Zest after a cell swap

The E110 Zest's fuel gauge IC retains the discharge curve of the old, degraded cell after replacement. When the new cell's open-circuit voltage drops through the range the IC has mapped as "near empty," the system triggers an emergency shutdown — even though usable capacity remains. This is not a defective cell. It is a coulomb counter calibration mismatch between the old curve stored in firmware and the actual voltage behaviour of the new cell. One full uninterrupted discharge-to-shutdown followed by a full charge cycle overwrites the stored curve and eliminates premature cutoffs.

E110 Zest not powering on after sitting in storage with a depleted battery

Li-ion cells stored fully discharged can drop below the BMS lockout threshold of approximately 2.5V per cell. When voltage falls this low, the protection circuit opens and blocks all current flow — including from the charger — so the phone shows no response on any cable. Connect the phone to a wall adapter and leave it untouched for 15–20 minutes. The charge IC on the E110 Zest applies a trickle pre-charge current that slowly raises cell voltage back above the BMS re-enable threshold. Once voltage reaches roughly 2.9V, the protection circuit closes and normal charging resumes.