ZDnet says that if not powered on, solid state disks are likely to forget their contents within a year or two, or faster if stored in warm conditions.

So if you store data on a shelf, don’t use an SSD or flash drive. Good old magnetic media is the best (as long as you keep something to plug it in to). Optical gives you a few years but is small and slow by current standards.

And turn on your old gadgets now and again, or you might as well have told me (I am very forgetful, being made of foam).