My apple watch is two years old and now after fully charged the battery lasts about 5 hours with minimal usage. Do I need to replace the battery? Is that possible? What is the cost and am I only able to use official Apple Store to accomplish this?

Hi

Battery life varies depending on use and other factors. Examples are detailed here:

Apple Watch - Battery - Apple

Apple's tips for maximising battery life on Apple Watch are detailed here:

Batteries - Maximizing Performance - Apple

If your Apple Watch experiences significantly shorter battery life than Apple's examples suggest that you should expect, then it may help to follow these steps, which have previously resolved battery life issues for other users, including after software updates when usage has not otherwise changed (check after each):

If you have not yet done so, update your iPhone and Apple Watch to the latest software, starting with your iPhone:

• Update the iOS on your iPhone, iPad, or iPod touch - Apple Support
• Update your Apple Watch - Apple Support

Restart both your iPhone and your Apple Watch, turning both off together and then restarting your iPhone first:

• Restart your iPhone, iPad, or iPod touch - Apple Support
• Restart your Apple Watch - Apple Support
• If the issue persists, check for and close any unresponsive apps on your iPhone and then restart both devices again.

If you have ever (not necessarily recently) previously used the Workout app and/or any third-party fitness or sleep tracking apps to record workouts on your watch, check on your watch to see whether there is a paused activity within any of them. If there is, end that activity from within the app on your watch (not your iPhone).

• If in doubt, remove any such third-party apps from your Apple Watch.

Unpair and re-pair your Apple Watch:

• The Watch app on your iPhone takes a backup of your watch automatically when unpairing via the app.
  • When setting it up again, initially choose to Restore from Backup. Most data and settings will be restored, with some exceptions (eg Apple Pay cards, passcode).
  • If the issue persists, consider instead unpairing and setting it up as a new watch.
• Unpair your Apple Watch and iPhone - Apple Support
• Set up your Apple Watch - Apple Support

Some users have previously experienced battery life issues in connection with using corporate profiles and/or Exchange Calendars. If you are using an Exchange Calendar, one or more of these steps may help:

• Archive your Exchange Calendar for all items before today.
• Remove / delete all old inbox messages relating to calendar invites (accept and decline notifications).
• Create a rule in your Outlook Mail account that moves all future accept and decline replies, immediately upon receipt, into a separate mail folder that does not sync with your iPhone and Apple Watch.
• Check your Exchange Calendar for errors.

Finally, it may help to:

• Remove third-party apps from the Dock and/or from your watch and then monitor battery performance after adding them back, one at a time:
  • Open apps
• Remove watch face complications and monitor battery performance as you add them back:
  • Change the watch face on your Apple Watch - Apple Support

Having tried the previous steps, if your remain concerned that battery life is shorter than it should be, then I suggest contacting Apple Support (remote diagnostics and/or mail-in service may be available, if required), making a Genius Bar reservation or visiting an Apple Authorised Service Provider for assistance:

• US: Apple Watch Service Answer Center - Apple Support
• Elsewhere: Select your country for Apple Watch service and repair information

If battery service is required, then prices in the US, for example, are detailed here:

Apple Watch Service Pricing - Apple Support

Yes make a genius bar appointment with Apple. They have tool to test your battery.