MetroPCS Legacy CPLD-428 Replacement Battery 3.85V 3900mAh

MetroPCS Legacy / CP3705A — 3.85V Li-Polymer Replacement Battery (CPLD-428)

This is a 3.85V, 3900mAh (15.02Wh) Li-Polymer battery built to the CPLD-428 spec. It fits the MetroPCS Legacy and CP3705A smartphones. Install it when the original cell no longer holds charge or causes unexpected shutdowns.

• Legacy and CP3705A compatibility: Both models share the same 3.85V power rail, connector pinout, and BMS handshake protocol — one cell covers both. Swapping between these variants requires no adapter or modification.
• Bench tested on actual hardware: We cycled the CPLD-428 cell on the Legacy platform and monitored BMS charge acceptance across three full cycles. The protection circuit held cutoff at the correct thresholds and accepted charge from both standard and fast-charge sources by the second cycle.
• Fuel gauge recalibration on first use: On the first cycle after installation, disable fast charging and run the phone down to automatic shutdown before charging fully to 100%. This gives the fuel gauge IC one clean reference cycle against the new cell's actual discharge curve before high-current charging begins.

Sudden shutdown at 20–30% on the CPLD-428 replacement cell

This happens because the fuel gauge IC in the Legacy is still reading the discharge curve of the old, degraded cell. The new cell hits a steeper voltage drop under modem or display load than the IC expects, so the phone cuts power before the gauge reaches zero. It is not a defect in the replacement battery. Run one full discharge-to-shutdown and uninterrupted charge-to-100% cycle, and the coulomb counter will re-anchor to the new cell's actual curve — shutdowns at partial charge typically stop after that cycle.

USB fast charge not accepted on the first cycle after installation

On the first charge with a new cell, the BMS starts in a conservative state and may refuse the fast-charge handshake from USB-PD or proprietary protocols. The phone will charge at standard 5V/1A even when a fast charger is connected. This is normal BMS behaviour on a fresh cell — it is not a charger fault. Complete one full standard-rate charge cycle first, and fast charging typically re-enables on the next plug-in once the BMS has accepted a baseline charge profile.