About this replacement
Panasonic KX-TU301 Series — 3.7V Li-ion Replacement Battery (CGA-LB102)
This is a 3.7V, 700mAh Li-ion replacement battery for the Panasonic KX-TU301 candybar mobile phone and related models. It slots directly into the KX-TU301, KX-TU301 GME, KX-TU321, and KX-TU311, among others. OEM part number CGA-LB102.
- KX-TU301 series compatibility: These models share the same battery bay dimensions, 3.7V nominal voltage rail, and CGA-LB102 connector pinout. The BMS handshake is identical across the range, so one cell covers the full group.
- Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on a KX-TU301 unit. The BMS accepted the charge handshake cleanly, voltage held steady at 3.7V nominal under load, and the phone registered capacity without error flags.
- Fuel gauge recalibration on first use: After fitting this cell, disable any fast-charge accessory for the first complete discharge-charge cycle. The phone's fuel gauge IC is calibrated to the old cell's discharge curve. One full cycle at standard current lets it recalibrate against the new cell before any high-current charging is applied.
Why the KX-TU301 reports wrong battery percentage after a cell swap
The phone's fuel gauge IC uses a stored discharge curve built from the original cell's behaviour over time. When you install a new cell, that curve no longer matches the actual charge state. The gauge reads percentage against old data, so it shows incorrect numbers — often jumping or sitting too high or too low. One complete discharge to auto-off followed by a full charge resets the coulomb counter and aligns the gauge to the new cell's actual curve.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC has not yet recalibrated and the displayed percentage does not reflect true cell voltage. The phone reads 25% but the cell has already dropped below the BMS cutoff threshold — around 3.0V under the load of an active call or screen wake. The BMS trips and the phone shuts off without warning. Run one full discharge-charge cycle at standard current first; after recalibration, the displayed percentage will track actual cell voltage and the shutdowns stop.