I have many bitcoin core wallets from years ago (encrypted). How do I check their balance from command line? Loading each one in bitcoin core GUI is a painfully slow process that will take weeks/months.
The command line will be as slow as the GUI when it comes with scanning a wallet file once you've loaded it, so querying for the balance using Bitcoin-cli will have the same pace as Bitcoin-qt.
If they were previously scanned with balance and history, then there should be readable addresses after the string:
name" when you open them with a text editor.
If not, all you'll see are 'jumbled' strings.