DS220j is tight but ever considered building your own? I did with an old pc and some freenas magic. way more customizable. but hey, welcome to the NAS club! it’s all fun and games till a drive fails haha.

If you got a multimeter, check the battery contacts for proper voltage. If that reads fine, the problem could be internal. I'd recommend checking out some teardown videos; you might find something is loose or needs a clean inside.

lol RIP. Should've named it RAID ¯\_(ツ)_/¯ not RAID 5.