BLU Pure XL Replacement Battery 3.8V 3500mAh Li-Polymer

BLU Pure XL — 3.8V Li-Polymer 3500mAh Replacement Battery

This is a 3.8V, 3500mAh lithium-polymer replacement battery for the BLU Pure XL smartphone. It slots into the Pure XL's battery bay and restores power to the processor, display, modem, and all other onboard components. Capacity is 13.3Wh, matching the original cell specification.

• Pure XL platform fit: The Pure XL uses a fixed-connector lithium-polymer cell with a specific footprint — 76.00 x 63.90 x 4.50mm. This battery matches that footprint exactly, including the BMS communication pins the charge IC expects to see on power-up.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Pure XL platform. The BMS handshake completed correctly on first boot, and the charge IC accepted the cell without fault flags or charging interruptions.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging begins on an uncalibrated counter.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity defect. A new lithium-polymer cell has a slightly different voltage-versus-charge curve than the aged cell the fuel gauge IC was calibrated against. Under peak modem or display load, the phone's voltage drops below the shutdown threshold before the percentage reading catches up. One full discharge-charge cycle at standard rate resets the coulomb counter and brings the reported percentage back in line with actual cell voltage. After calibration, shutdowns below 20% stop.

OS reporting wrong battery percentage after cell swap

The fuel gauge IC on the Pure XL stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage profile, so the percentage display jumps or reads inaccurately. Drain the battery until the phone shuts down on its own, then charge uninterrupted to 100% without fast charging enabled. After one complete cycle, the coulomb counter recalibrates to the new cell and percentage reporting stabilises.