I think that’s just a too advanced threat you want to handle. If you are facing such an opponent, you shouldn’t let your hardware out of your hands at any time.

I think that’s just a too advanced threat you want to handle. If you are facing such an opponent, you shouldn’t let your hardware out of your hands at any time. You can probably replace the battery by a smaller model and put a keylogger in the remaining space. There’s just no way to prevent hardware modification without using tamper evident seals on all openings, and even that probably isn’t 100% safe.