About this replacement
Nokia 105 4G (2021) — 3.7V Li-ion Replacement Battery (BL-L5G)
This is a 3.7V, 800mAh Li-ion replacement battery for the Nokia 105 4G (2021). It uses OEM part number BL-L5G and fits the 2021 revision of the 105 4G directly. The Nokia 105 4G is a basic mobile phone built for calling and SMS — not a smartphone — so its battery demands are low-current and steady.
- Nokia 105 4G (2021) fitment: The BL-L5G connector pinout and physical dimensions (53.10 × 33.80 × 5.50mm) match the 2021 model's battery bay. Earlier 105 variants use different cells — confirm your model reads "105 4G" on the back label before ordering.
- Bench tested on actual hardware: We cycled this cell through full discharge and recharge on the Nokia 105 4G platform. The BMS accepted charge without flagging a fault, and the fuel gauge IC began tracking capacity correctly after one complete cycle.
- Fuel gauge recalibration after install: Run one full discharge to low battery warning, then charge uninterrupted to 100% before normal use. The 105 4G's fuel gauge IC calibrates its coulomb counter against the new cell's discharge curve during that first cycle — skipping it causes erratic percentage readings early on.
Why the Nokia 105 4G reports wrong battery percentage after a cell swap
The 105 4G stores its fuel gauge calibration data against the original cell's discharge curve. When you fit a new BL-L5G cell, that stored curve no longer matches the new cell's actual voltage-to-capacity relationship. The result is percentage readings that jump or stall — most often between 40% and 70%. One complete discharge-charge cycle overwrites the calibration and brings the percentage display back into line.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC hasn't finished recalibrating and calls shutdown too early based on stale voltage thresholds. The cell's actual voltage drops faster than the uncalibrated gauge expects under call load, triggering a protective cutoff. It is not a faulty cell — it resolves after one full cycle. Charge to 100%, confirm the phone reads a full bar, then use normally.