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

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

This 3.7V 800mAh (2.96Wh) Li-ion cell replaces the original battery in the MetroPCS CDM-7126 and CDM-7126m handsets. Both models share the same battery bay dimensions and connector pinout — 54.09 x 34.88 x 4.40mm. Fit and voltage match the factory spec exactly.

• CDM-7126 and CDM-7126m compatibility: Both variants use the same physical battery form factor, contact layout, and 3.7V nominal voltage rail. No adapter or modification is needed — the cell drops into either bay and makes full contact with the phone's charge IC.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the bench. The BMS accepted charge from the CDM-7126 charge controller without fault flags, and the protection circuit tripped correctly at both low-voltage cutoff and overcurrent thresholds.
• Fuel gauge recalibration on first use: On first installation, disable any fast-charge mode and let the phone complete one full discharge-to-charge cycle before normal use. This gives the fuel gauge IC time to map the new cell's discharge curve — skipping this step is the main reason the percentage counter reads inaccurately after a swap.

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

This is a voltage cliff issue, not a capacity problem. Under modem transmit load or screen-on current draw, the new cell's terminal voltage drops faster than the fuel gauge IC expects — because the IC is still running the discharge curve from the old, degraded cell. The phone's low-voltage protection interprets this sag as a dead cell and cuts power even though charge remains. One complete unconstrained discharge-charge cycle resets the coulomb counter and maps the new curve. After that cycle, shutdowns at 20–30% typically stop.

Phone warm near the battery compartment during first charge

A new Li-ion cell has higher internal impedance than a cell that has completed several cycles. During the first charge, the charge IC pushes current into that higher-impedance cell and generates more heat than users expect. This is normal and fades after two or three cycles as impedance drops. If the phone stays warm beyond the third full charge, check that the charge controller is not stuck in fast-charge mode — set charging current to standard and confirm the phone idles below 40°C at the battery cover.