The Citizen Eco-Drive line of watches uses a solar panel to charge its battery, allowing it to run for long periods without needing to be actively recharged. Unlike older solar watches, Eco-Drive watches have no visible solar panel, absorbing light energy directly through the watch's dial. Keeping one of these watches charged requires only that you expose it to sunlight -- or another light source if this isn't possible -- regularly.
Put your watch in direct sunlight as frequently as possible. The rate of charge and battery life will depend on the model, but for most Eco-Drive timepieces a few minutes of sunlight each day will be sufficient. Just leaving your watch on a sunny windowsill while you take care of another task will be enough for most purposes.
Lengthen your watch's exposure if the weather is cloudy. Get outside as much as possible while wearing your watch, and leave it in a location that receives natural light when you are not. Even with reduced sunlight, an hour's exposure should keep your watch running for days at a time.
Expose the watch to fluorescent light if sunlight is not available. Place the dial close to the light -- around eight inches is a good distance -- and allow it to charge. Fluorescent light will provide as much charge as indirect sunlight; even an hour's exposure should give you around a week's worth of charge. Again, the exact charge rate will vary depending on the watch.
Avoid charging your Eco-Drive watch with an incandescent bulb; prolonged exposure to an incandescent light within about 50 cm (20 inches) may expose the watch to excessive heat. Similarly, very warm, sunny environments such as locked cars or greenhouses can cause damage.