The red LED light on the CH100 or PS100 comes on whenever there is a working charging source connected. For example, if a solar panel is connected to the device, and the sun is shining, the LED light will turn on until the sun starts to go down. The red LED light should always be on when the device is connected to the wall transformer (when the ac power is present). Thus, the LED light is only a confirmation of power available to charge the battery.
If it is desirable to have an indication that the power switch is on, an LED light can be added to an unused control port on the datalogger and a program can be written to cause the LED light to blink every few seconds. Blinking the LED light once every few seconds will not put a large load on the battery, whereas a continuously lit LED draws down the battery more quickly.