Fairphone F1B101 Replacement Battery 3.7V 1500mAh

Fairphone FP1 Series — 3.7V Li-ion Replacement Battery (F1B101 / F1B201)

This is a 3.7V Li-ion replacement battery rated at 1500mAh (5.55Wh) for the Fairphone FP1 smartphone. It fits devices listed under model numbers F1B101 and F1B201. Swap it in when the original cell no longer holds a charge or the phone shuts down unexpectedly under load.

• FP1 platform fit (F1B101 / F1B201): Both model codes reference the same FP1 hardware generation. The connector pinout, cell dimensions (51.30 × 50.80 × 5.60mm), and BMS handshake are identical across the run, so one cell covers both variant codes without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on an FP1 unit. The BMS accepted the cell without error flags, charge termination fired correctly at 4.2V, and protection tripped as expected on an overcurrent draw test.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one full discharge down to automatic shutoff, then charge uninterrupted to 100%. This gives the FP1 fuel gauge IC one complete cycle to map its coulomb counter against the new cell's discharge curve before normal use.

Sudden shutdown at 20–30% on the Fairphone FP1

The FP1's fuel gauge IC builds its percentage estimate from a discharge curve stored during previous cycles. When an aged original cell is replaced, the stored curve no longer matches the new cell's voltage-to-capacity relationship. Under a spike load — screen on full brightness, active data connection, GPS — the new cell's terminal voltage can drop sharply below the cutoff threshold even while the reported percentage reads mid-range. The fix is one full unconstrained discharge-to-shutoff cycle followed by a full charge. After that single cycle the gauge IC resets its reference points and shutdowns at falsely high percentages stop.

Phone won't power on after the battery sat discharged in storage

Li-ion cells that drop below roughly 2.5V trigger a BMS lockout — the protection circuit opens to prevent cell damage, and the phone shows no response to the power button or charge cable. Plug the phone into a wall charger (not a PC USB port) and leave it for 15–20 minutes without touching it. The charger pushes a trickle current that brings cell voltage back above the BMS re-enable threshold, at which point the circuit closes and normal charging resumes. If the phone still shows nothing after 30 minutes on a wall charger, check the cable and adapter with a known-good device before drawing any conclusion about the cell.