Motorola PEBL U6 BR50 Replacement Battery 3.7V 710mAh

Motorola PEBL U6 / Razr V3 Series — 3.7V Li-ion Replacement Battery (BR50)

This is a 3.7V, 710mAh Li-ion cell that replaces the BR50 battery in the Motorola PEBL U6 and Razr V3 series flip phones. It fits the Razr V3c, V3i, and V3m among others using the same BR50 footprint and connector. Capacity figure is 710mAh as listed in the product specification — not the inflated numbers sometimes quoted on grey-market listings.

• PEBL U6 and Razr V3 series fit: These models share the same battery bay dimensions, 3.7V single-cell architecture, and two-pin connector layout. Any phone in this cluster drawing from the same BR50 platform accepts this cell without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a PEBL U6 unit. The BMS accepted the charge IC handshake on the first cycle and held voltage above 3.5V under normal screen and standby load.
• Fuel gauge recalibration on first use: On first use after installation, run one complete discharge down to automatic shutoff, then charge uninterrupted to 100% without interruption. The phone's fuel gauge IC needs this full cycle to map the new cell's discharge curve — skipping it causes erratic percentage readings for days.

Why the PEBL U6 reports wrong battery percentage after a cell swap

The PEBL U6 uses a fuel gauge IC that stores the discharge curve of the original cell in memory. When you install a new cell, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The phone reads voltage and maps it to the old curve, producing percentage figures that are off by 10–20%. One full discharge-charge cycle forces the IC to recalibrate against the new cell's actual curve, after which percentage reporting stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC is still running the old calibration and the cell hits its voltage cliff earlier than the phone predicts. The Razr and PEBL platform draws a spike of current when the radio transmits or the backlight fires — if the cell voltage drops below roughly 3.2V under that load, the BMS trips and the phone shuts off even though the displayed percentage looks safe. Run the full recalibration cycle first. If shutdowns persist after one full cycle, check that the battery contacts on the phone are clean and making firm contact — a resistive connection accelerates voltage sag under load.