
Knowing what those little lights on the Kobalt 40V charger mean can help you avoid a lot of guessing. I decided to check the various signs to understand exactly what each of them wants to say. When I placed a partly charged 2.5Ah battery, the light flashed green (that shows that the battery is charging).
The green light was steady and regular not random or fast. It seems to be easy to watch the process of charging.

Leaving the battery on the charger a bit of time did its job. Soon after, that flashing green light became permanent, steady glow, marking that the battery reached its maximum charge. Curious, I quickly checked the reading myself.
All tiny green strips lit up, showing that it is ready to use at full capacity. I lkie, when the technology simply works like this, as it should.
Kobalt 40V Charger LED Indicator Guide

The tests turned mainly around what happens when the temperature gets too hot or too cold. Those batteries can be genuinely tricky about charging (if they are too hot or too cool), they simply refuse and shut down. Thanks too it, the Kobalt charger has a helpful way to tell you about the situation.
The LED indicators change to solid red if the battery is in a bad temperature range. No flashing red light to warn you, but permanent, steady red. I learnt that the hard way, when I tried to charge a battery that sat outside in the heat.
The charger simply said "no" and showed that permanent red signal.

The battery needs to cool to room temperature before the charging can start. No reason for worry, though, the charger is built to protect the battery and will not charge it if the temperature is outside of limits. When it returns to normal level, the solid red light goes away and the usual flashing green sign restarts, showing that the charging continues.

There is one more light pattern that sometimes appears and that genuinely worries me. Really, whatever the cause, if you see that flashing red, the charging simply will not happen. But well, at least the charger is smart enough to catch such errors and protect your battery against bigger damage.

Flashing red light on your charger does not always show that the battery is done. Sometimes a simple reset can fix the problem. Take the battery fully out, wait ten seconds, then put it back flat.
That can clear possible errors that caused the red glow. Even so, if the light stays after a reset, probably the battery has a more serious problem that needs attention orreplacement.The various light signs on the Kobalt charger turn out to be a pretty simple system of talking, when you understand it.