How can you tell if an ecco citizen watch battery needs to be replaced?

You can tell if an Ecco Citizen watch battery needs to be replaced if the watch stops running or if the hands are moving erratically. Additionally, if the display is dim or fading, it may indicate a low battery. Regularly check for any signs of corrosion around the battery compartment as well, which can also suggest that a replacement is needed. If you're unsure, it's best to take the watch to a professional for assessment.