[Ziggythewiz]

I don't know enough about lithium to know cell failure behavior, but with lead you see it first as extra sag while in use, but just checking voltage along the string wouldn't do much (aside from balance checking). I think if you could move it every day or two it'd be great for you to get familiar with typical sag on an individual cell in use, and then you'd be better able to spot one with issues.