On your Adventurer or Adventurer 2 watch, there is a light indicator on the charger. Without plugging the watch in, the light will be green to show there is power to the charger.
When your watch is being charged, the light indicator will normally be red.
Sometimes, if your watch battery is extremely low, you will see the charger flash red and green. This is because the battery levels are so low that it needs to be charged slowly to protect the battery. Once the battery has enough charge, it will be charged at the normal rate, making the light indicator a solid red again.
Once the watch is fully charged, the indicator will be a solid green to show it's done.