A recent incident involving a Reddit user erased his Android backup on Google servers after not using his Android phone for two months.
Google keeps a backup of everything we link it to — that is what most Android users perceive. Reddit user Tanglebrook also believed that until his backup data was erased from Google. His crime was that he switched to an iPhone for two months, which is the exact period Google keeps a backup of your Android phone before it considers it as inactive and kicks it out of your server. The result was that he had to start using his Nexus 6P again as a completely new Android phone user after switching back.
This report from Android Headlines also mentions that the concerned person wasn’t notified of any of this background activity in any way. Tanglebrook also discussed the matter with a Google representative and found out that there was no way to keep the backup on his Google Drive or any other place.
Google’s official policy (read here) states that a backup for a particular user is marked for expiration if the servers find the data unused for two weeks or found ‘inactive’. When users import data from an old Android phone to a new Android phone, the servers treat the new device as the active device and thus treat the account active. Also, if any Android device registered to a particular account gets additional data such as new contacts or any other new settings, it is automatically synchronised with other devices as well.
This means that Google servers constantly keep checking every account for checking the status of the devices. Since Android’s backup cannot be used on other platforms, the only way to retain your Android’s backup is to keep the device active by letting it connected to Google’s servers, i.e. keep the Android phone connected to an Internet connection.