SD cards are one of the most volatile mediums for data storage. Flash memory in general runs the risk of discharge over time. Being powered every now and then can help IIRC.
I’ve looked into long-term data hoarding and found that there’s not too much consensus on the best mediums. They all have their problems. Most turn their noses up at the idea of a set-it-and-forget-it system, preferring laboriously maintained arrays of HDDs. These fail somewhat regularly so they maintain multiple backups and plan/build around that.
I like optical media, but its problems include high cost per GB, taking up significant physical space, the inability to rewrite data, slow speed, and the waning availability of disk drives. Its longevity also depends on the specific technology the disk uses. Some disks are chemically active and the chemicals can break down over time. These can have comparable life to just storing it on a USB drive or something, so I wouldn’t bother with those.
I’ve been using discs specifically made for longevity called M-DISCs. They are supposedly chemically inert and can last for hundreds of years. They’re expensive compared to normal BDXLs, you need a bluray drive rated for burning them, and some people say they’re hokey…their lifetime claim is pretty lofty, to be fair. I also use archival gold DVDs (4.7GB) for smaller files.
Its slow as shit for whatever reason. Less than 1x speed by its own metrics. There may be a problem somewhere, but I don’t care about speed as much as accuracy and not ruining disks, so I haven’t looked into it.