LG KW730 Replacement Battery 3.7V 1500mAh BF-45FN

LG KW730 — 3.7V Li-ion Replacement Battery (BF-45FN)

This is a 3.7V, 1500mAh Li-ion replacement battery for the LG KW730 smartphone. It uses OEM part number BF-45FN and slots directly into the KW730 battery bay. Capacity is rated at 5.55Wh, matching the original cell specification.

• KW730 battery bay fit: The KW730 uses a removable Li-ion pack with a three-contact connector carrying positive, negative, and a BMS data line. The BF-45FN replicates this contact layout and communicates cell status back to the phone's charge IC — the phone recognises the pack and begins charging without error flags.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a KW730 unit. The BMS held the charge cutoff at 4.2V and the low-voltage cutoff triggered correctly before the cell voltage dropped below 3.0V. No false charge-complete signals were observed.
• First-cycle fuel gauge reset: On first use, disable fast charging if your KW730 supports it, then run one complete discharge-to-charge cycle. The fuel gauge IC on the KW730 was calibrated to the original cell's discharge curve. One full cycle lets it recalibrate against the new cell before normal use.

Sudden shutdown at 20–30% on the KW730 after a cell swap

This happens because the fuel gauge IC is still using the discharge curve from the old, degraded cell. A fresh cell holds a higher voltage at any given state-of-charge, so the IC misreads remaining capacity. Under modem or screen load, the phone draws enough current to cause a brief voltage sag — the IC interprets this as a critical low-voltage event and shuts down. One full discharge cycle to around 3.4V under normal use, followed by a full charge, resets the coulomb counter to the new cell's actual curve.

KW730 not powering on after the replacement battery sat in storage

Li-ion cells self-discharge during storage. If the BF-45FN cell drops below 2.5V, the BMS trips its deep-discharge lockout and the phone will not respond to a normal power-on press. Connect the phone to a charger and leave it for 15–20 minutes without attempting to power it on — the charge IC needs to trickle current into the cell at a low rate before the BMS re-enables the output circuit. Once the cell recovers to approximately 3.0V, the phone will power on normally.