How long can I store a new lithium battery before installing it?

Not an expert on parts storage, so anyone else please correct me - but as long as you have it in a dry, not overly hot (don't stick it somewhere with direct sunlight/high humidly/its for some reason over a 100(?) degrees F and I'm guessing the shelf-life shouldn't be altered from whatever the manufacturer norm is.

Which if I had to guess, is a couple years?

Not certain, just going off intuition here but I can't see why a spare battery kept in the box and in safe, standard storage would have any degradation. Especially ordering an EOM from Dell.