I have a Steinberger Spirit as a backup bass. Takes up almost no space—in fact, between gigs it lives in the back of my car. It’s passive, so no batteries. The Steinberger bridge holds tuning for days, so it can be grab-and-play. No, it doesn’t by any measure sound like my regular basses, but that’s not the point. The point is to keep the music going.
I’ve had it for at least ten years. Haven’t needed to use it onstage even once, but it’s a cheap insurance policy. Bonus: since it lives in my car, it’s come in handy for impromptu jams and practice sessions.