Fly IQ245 Replacement Battery BL4237 3.7V 1300mAh

Fly IQ245 / IQ430 Series — 3.7V Li-ion Replacement Battery (BL4237)

The BL4237 is a 3.7V, 1300mAh Li-ion cell that fits the Fly IQ245, IQ246, IQ245 Wizard, IQ430, and related models. It powers the phone's processor, display, modem, and all onboard communications. Capacity figure is taken directly from product data at 4.81Wh.

• IQ245 / IQ430 platform compatibility: These models share the same battery bay dimensions and 3.7V voltage rail. The BL4237 connector pinout and cell thickness — 4.45 mm — match across the series, so no physical modification is needed at installation.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the IQ245 platform. The BMS accepted the charge current without trip events, and protection thresholds activated correctly at the low-voltage cutoff point.
• Fuel gauge recalibration on first use: On first installation, disable fast charging if available and run one complete discharge-charge cycle before normal use. The phone's fuel gauge IC is calibrated to the original cell's discharge curve — a full cycle against the new cell lets it re-anchor the coulomb counter and report accurate percentages from the second cycle onward.

Sudden shutdown at 20–30% on a replacement cell in the IQ245

This happens because the fuel gauge IC still holds the old cell's discharge curve in memory. When the modem or display pulls a load spike, the new cell's actual terminal voltage drops below what the old curve predicts for that percentage. The phone interprets this as an unexpected undervoltage condition and shuts down immediately. One full discharge-charge cycle overwrites the stored curve reference and resolves the premature cutoff.

Phone feels warm near the battery slot on the first two charges

A fresh cell has higher internal impedance than a worn one. The charge IC pushes its standard current into a cell that hasn't yet been conditioned, which generates more heat across that impedance. This is normal for the first one to two cycles and reduces as the cell settles. If the case stays hot after three full cycles, check that the charge IC isn't stuck at maximum current — pull up battery settings and confirm the temperature reading drops below 35°C during charging.