ZTE F290 Replacement Battery 3.7V 800mAh Li3709T42P3h463657

ZTE F290 / N281 / Z221 / Z222 — 3.7V Li-ion Replacement Battery (Li3709T42P3h463657)

This is a 3.7V 800mAh (2.96Wh) Li-ion cell for the ZTE F290, N281, Z221, and Z222 candybar-style phones. It replaces OEM parts Li3709T42P3h463657 and Li3708T42P3h463657. The cell fits the original battery bay without modification and connects through the same three-pin contact strip.

• F290 / N281 / Z221 / Z222 platform fit: These four models share the same battery bay dimensions (46.26 × 35.60 × 5.68mm), voltage rail, and three-pin connector layout. The BMS handshake uses the same thermistor pin arrangement across the group, so one cell covers all four.
• Bench tested on actual hardware: We cycled this cell on the F290 platform and confirmed the BMS accepted the cell on first insertion, charge current ramped correctly through CC/CV phases, and the protection circuit tripped at expected low-voltage cutoff without locking the board.
• Fuel gauge recalibration on first cycle: After installation, run one full discharge to automatic power-off, then charge uninterrupted to 100% before normal use. The phone's fuel gauge IC was calibrated to the old cell's discharge curve — one complete cycle resets the coulomb counter against the new cell so percentage readings stay accurate.

Sudden shutdown at 20–30% on the replacement cell

The ZTE F290's fuel gauge IC maps a voltage-to-percentage curve learned from the previous cell. A new cell has a flatter discharge curve and holds voltage higher for longer before a sharp drop. When the phone expects 20% remaining but the new cell is already near its voltage cliff, the modem or display load pulls current the cell can't sustain at that state of charge — the phone shuts off instantly. One full discharge-charge cycle lets the coulomb counter relearn the curve. After that cycle, shutdowns below 20% stop.

Phone not powering on after the battery sat in storage

Li-ion cells self-discharge at roughly 2–3% per month. If the replacement cell sat in a warehouse for an extended period before you received it, the cell voltage may have dropped below 3.0V — the threshold where the BMS enters lockout to prevent damage. The phone will show nothing when you press power or plug in a charger. Connect the phone to a charger and leave it for 20–30 minutes without pressing any buttons; the protection circuit allows a trickle current below 3.0V to recover the cell. Once voltage climbs above 3.0V, normal charging resumes.