The 18V ONE+ Charger, Fast Charger, and 8A Rapid Charger are the most basic battery chargers in the line, each able to handle one battery at a time. They also have identical LED indicator lights.

After plugging the 80V charger into a wall outlet, the red LED should turn on and remain steady. It should stay solid until a battery is plugged in, at which point the other LEDs will come into play.

Ryobi batteries do have their problems, but accidentally (or even purposely) leaving a lithium battery on its charger is generally no more or less dangerous than leaving any electronic device ...