TP4056 CHRG LED stays on for hours — is the charge ever going to terminate?

Six or seven hours for a 2000 mAh cell isn't obviously wrong, but it depends heavily on what the PROG resistor on that module is set to.

The TP4056 charges in two phases — constant current (CC) until the battery reaches 4.2 V, then constant voltage (CV) at 4.2 V until the current naturally drops off as the cell fills. The CHRG LED stays on through both phases. It only goes out when the charging current falls below about 10% of the programmed charge rate. That CV tail takes time, especially at lower charge currents.

Finding your charge current

The PROG pin resistor sets the charge current. Most stock blue TP4056 modules ship with a 1.2 kΩ resistor, which gives roughly 1000 mA (1 C for your cell). At that rate, 2000 mAh should hit 4.2 V in around two hours, then spend another hour or so in CV taper. If you see a 2 kΩ or 3 kΩ resistor instead, the current is 600 mA or 400 mA respectively — the CC phase alone stretches to five hours or more.

Measure RPROG with a multimeter (it's the only resistor on the board, near the PROG pin) to confirm what you're actually charging at.

What to check if it's been six-plus hours and still charging

Find your multimeter probe. Once you have it:

1. Measure the BAT pin voltage. If it's still below 4.1 V, the CC phase isn't finishing — either the charge current is too low for that cell, or there's high internal resistance in an old salvaged cell.
2. If BAT is sitting at 4.2 V but the LED is still on, you're in the CV phase and the current hasn't dropped far enough for termination. This can happen with a degraded cell whose internal resistance is high enough that the termination current threshold never quite triggers.
3. Check the TEMP/NTC pin. Some modules leave this floating, which is usually fine; others have a thermistor pad. If the TEMP pin voltage is outside the TP4056's acceptance window, charging suspends and can behave oddly.

The CC/CV charging process explains what the charger IC is actually doing in each phase if that helps fill in the picture.

One thing to note: salvaged cells from old power banks can have elevated internal resistance and may not accept a full charge normally. If the cell is a few years old and has been through a lot of cycles, that might be contributing.