About this replacement
Nokia C20 Plus (TA-1388 / TA-1380) — 3.85V Li-Polymer Replacement Battery (SP410)
This is a 3.85V, 4850mAh Li-Polymer battery for the Nokia C20 Plus smartphone, covering variants TA-1388 and TA-1380. It replaces OEM part SP410 and fits directly into the original battery bay. Capacity figures are drawn from product data — 18.67Wh total energy at rated voltage.
- C20 Plus variant coverage (TA-1388, TA-1380): Both TA variants share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The SP410 cell communicates with the phone's fuel gauge IC over the same data line across all C20 Plus units, so a single cell covers both regional variants without modification.
- Bench tested on actual hardware: We ran the SP410 replacement through a full charge cycle on a C20 Plus unit. The BMS accepted the charge without fault flags, voltage climbed to 4.35V at cutoff, and the fuel gauge IC registered the cell without requiring a manual reset cycle before first read.
- First-cycle fast charge guidance: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's actual discharge curve before high-current charging pushes current into an uncalibrated cell.
Why the C20 Plus reports wrong battery percentage after a cell swap
The C20 Plus uses a coulomb-counting fuel gauge IC that builds its capacity model from previous charge and discharge cycles. When you swap cells, the IC still holds the old cell's discharge curve in memory. It maps the new cell's voltage against that stale model, so the percentage readout drifts — often reading 20% too high or too low. One full uninterrupted discharge to automatic shutdown, followed by a full charge to 100%, forces the IC to write a new curve against the SP410 cell. After that cycle, percentage accuracy stabilises.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC hasn't recalibrated and the new cell hits a voltage cliff — typically around 3.5V — while the screen and modem are drawing peak current. The phone reads 25% but the cell voltage collapses below the BMS cutoff threshold under load. The fix is the same full recalibration cycle: drain the phone to shutdown, charge uninterrupted to 100%, and let the coulomb counter reanchor to the new cell. If shutdowns persist past two calibration cycles, check that the battery connector is fully seated — a loose pin causes voltage drop that mimics the same symptom.