Hi

That symbol means that your watch is currently charging, but the battery charge level is presently low.

Leave your watch on the charger for at least 2.5 hours - and perhaps for longer (such as overnight).

You can tap on the screen at any time to check on charging progress.

green lightening bolt generally means you are charging.

Is there something abnormal with the charge?

When charging your watch, check that:

• All plastic wrap has been removed from both ends and both sides of the charging cable (check closely on the head of the charger).

• The back of your watch and the head of the charging cable are clean and dry (clean them with a nonabrasive, lint-free cloth).
• The charging head is properly aligned with the back of the watch, with the concave / curved side touching it fully:
  • Some watch docks, stands, cases or protectors might hinder this. If you are using any of these accessories, try instead charging the watch by connecting it directly to the charging cable, without using them.
• If possible, test by using another genuine Apple Magnetic Charging Cable (for example, by borrowing one from a friend).
• If you are charging your watch by plugging the cable into mains power:
  • Check that the USB connector on the Apple Magnetic Charging Cable is pushed fully into the USB Power Adapter.
  • Check that the USB Power Adapter is pushed fully into the power outlet.
  • Try using different adapters from the following:
    • The Apple USB Power Adapter that was supplied with the watch, or;
    • An Apple 5W (iPhone) or 12W (iPad) USB Power Adapter, or;
    • An Apple-certified (MFi) third-party 5W USB power adapter.
  • Try using a different power outlet (one that is known to be working properly).
• If no other suitable power adapters are available, try instead charging by plugging the cable into a USB port.
  • If charging via a USB port on a computer, ensure that you use a USB 2.0 or 3.0 port, the computer remains turned on and awake and the cable is plugged directly into the computer (not into, for example, an external keyboard).

After charging, if your watch has not already restarted automatically, remove it from the charger and:

• Try restarting it (by pressing and holding the side button until you see the Apple logo).
• Next try force restarting it: press and hold both the side button and Digital Crown for around 10 seconds, until you see the logo.

If you identify an issue with a particular component (adapter, cable or watch) or if the issue otherwise persists, contact Apple Support (mail-in service may be available) or make a Genius Bar reservation with a view to having your product(s) checked (under warranty, if eligible):

• Contact - Official Apple Support
• https://twitter.com/applesupport
• http://www.apple.com/retail/geniusbar/

To check your warranty status (the serial number is on the back of your watch):

• https://checkcoverage.apple.com/

More information:

Check your battery and charge your Apple Watch - Apple Support

If your Apple Watch won't charge or it won't turn on - Apple Support

Please follow the steps in my previous reply.

Your watch certainly should not need to be charged for two days or longer.

After following the suggested steps, if the issue is not resolved, contact Apple Support or make a Genius Bar reservation (via the links in my earlier reply).