Ring bell 2 loosing charge quickly.

I have had my ring door bell 2 for just over 1 month. I have charged it now 4 times. Im very disappointed with the product. I have called the support centre they tell this is normal after one hour on the phone. They want to charge me full retail price for upgrade to wired version. Any one know if 18v 500ma transformer will work with my door bell 2.