CHB, I'm not sure where you got that from, but you can store LiPos with any amount of charge in them, providing that they aren't left too long with very little charge (internal resistance, while low, does eventually discharge the pack).
80% or even fully charged is fine for 'storage', but if you're only leaving it for a week or so, the 50%ish that is left in the pack after your last run would be enough.
There is no 'optimal' storage charge, just don't leave a pack with no charge left in it. The 'optimal' charge idea is just made up for those people who are used to the habits of NiMH.
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