For the true paranoids, your battery bank also runs firmware... But realistically, a battery bank seems like an even better solution than a dedicated "USB cond

For the true paranoids, your battery bank also runs firmware... But realistically, a battery bank seems like an even better solution than a dedicated "USB condom"; it'll even protect you from "USB killer" attacks that inject high voltage to the ports, by frying just the power bank not the real device. It's more bulky than just a dedicated cable, though.