Well if Garmin doesn't have anything to help, then try disabling certain features in the phone app and maybe you can narrow it down. Hopefully it is something you really don't care about.

Have you had the 530 for a while and have a lot of rides on it? If you just started using the app, then maybe it's sending all those stored ride to the Garmin Connect website. So maybe it's just a temporary thing. Does the phone app also have the ability to update maps and stuff on your device? That too might be battery drain.