Should the battery be fully discharged? Fully charged? Removed from the radio?
While the admonition to store them lithium-based batteries at 40% DOD is a good one, how do you know since the discharge curve is essentially flat, and hence going by voltage alone will not tell you much if your radio has a voltmeter. You may be able to use the radio's own battery icon to get somewhere near the middle after some use.
You could calibrate it by knowing that if you get 8 hours of life on rx-only, then starting from a full charge and leaving the radio on for 4 hours will get you in the ballpark somewhere near 50% DOD. It is not *that* critical to be perfectly dishcarged to 40%.
BUT THE BIGGER PROBLEM is that most modern radios have "soft" power switches that are constantly polled for activity when the radio is off. This is a tiny amount of power, yet over time it will drain your pack much faster than if it was removed from the radio completely. AND if you stored your pack at near a half-discharged point, you may end up discharging the batteries so much that they fail in a relatively short amount of time.
Wouxon radios, even though they have what appears to be a hardware-based power switch with a solid click action, still do the same! Thus if you store your lithium batteries in the Wouxon, they will discharge in the radio very quickly. The best bet here is to discharge them as close to 50% dod if you can and THEN pull them from the radio.
The Wouxon is just one example, so the moral is once you have discharged your batteries by say half, pull them from the radio. At the very least, if for some reason you don't have time to discharge them very much, just try to get used up a bit if they had just been fully charged and pull them for storage.
Storing them fully charged for more than about 2 or 3 days starts to hurt them, but if left in the radio, the catch 22 is that the slow soft-power switch drain actually prevents this damage!
However, aside from total discharge, the worst thing you can do is charge them fully and pull them from the radio. Be sure to discharge them about half-way first.