Each Android WhatApp user has an account and a storage area inside the Google's Drive cloud. WhatApp data is always backed to your cloud taking the space available. Facebook company that owns the WhatsApp application reached an agreement with Google to make that service completely free.
This will not touch the Apple users of the application since they have their own servers and Data is stored in iCloud
Note: Messages that have not been updated for more than a year period will be wiped out. Connect your phone to a wifi for a large upload to the Cloud.