Try your carrier

Take the phones back to the cell phone carrier. They have a lot of adapters that should fit all of your old phones. At least they could power them up and maybe help delete your personal information. Or they may have a battery that will fit the phone and borrow the battery long enough to power up and delete your info. On the old feature phones the only information stored are the contacts and that is mostly cell phone numbers that don't belong to your friends anymore.