UTStarcom CDM-7126 Replacement Battery 3.7V 800mAh Li-ion

UTStarcom CDM-7126 / CDM-7126m — 3.7V Li-ion Replacement Battery

This 3.7V, 800mAh Li-ion cell replaces the original battery in the UTStarcom CDM-7126 and CDM-7126m mobile phones. Both models share the same battery bay dimensions and connector, so one cell covers either variant. Capacity figures here come from product data — 2.96Wh total energy.

• CDM-7126 and CDM-7126m compatibility: Both variants use the same 54.09 × 34.88 × 4.40mm footprint and the same connector pinout. The BMS voltage rails match across both production runs, so no modification is needed when fitting this cell to either model.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the CDM-7126 platform. The BMS accepted the cell without flag errors, and the charge IC completed a full CC/CV cycle without interruption.
• Fuel gauge recalibration on first cycle: After fitting this cell, run the phone down to auto-shutdown on normal use, then charge uninterrupted to 100% before unplugging. The CDM-7126's fuel gauge IC calibrates its coulomb counter against the actual discharge curve of the new cell — skipping this step causes the percentage display to drift or read incorrectly for several subsequent cycles.

Sudden shutdown at 20–30% on the CDM-7126 after a cell swap

A fresh Li-ion cell has a slightly different voltage-discharge curve than the aged cell it replaces. The CDM-7126's fuel gauge IC still holds the old curve in memory, so it miscalculates remaining capacity. Under any load spike — an incoming call, a screen wake — the cell voltage drops below the BMS cutoff threshold before the gauge expects it. The phone shuts down even though the display showed charge remaining. One full recalibration cycle — full discharge to auto-shutdown, then a full uninterrupted charge — overwrites the old curve and resolves this.

Phone shows 0% and won't power on after sitting unused for months

Li-ion cells self-discharge during storage. If the CDM-7126 sat with its original battery inside for an extended period, the cell voltage may have dropped below 2.5V — the point at which the BMS locks out to prevent damage. The phone won't respond to a power button press and may not show any charging indicator when plugged in. Connect the phone to a wall charger and leave it for 20–30 minutes without pressing anything; the charge IC trickle-charges at low current to bring the cell back above the 2.8V recovery threshold before normal charging resumes. If no indicator appears after 45 minutes, the cell is below recoverable voltage and the replacement cell in this listing is the correct next step.