Im no expert on this... but base on the characteristic of a lipo... don't make it below 3.0v. So if you store it, it will have a small drain of power... so as long as they don't go below 3.0v it should be okay.

As such, I'd rather store them with 100% or max power in it.

BTW I used to have a lipo that I have forsaken for more than two months... voltage droped to 2.4v if not 2.6v (in one of its cells)... at first I had problem recharging it back to life... so I simply slow charged that cell (0.2Amp max setting) with my B6 set on Auto. When it reached a little more than 3 volts, I stopped the single cell charging and rewired it to be balanced charge (it was 2s1p with 7.4v) normally.

Now that battery is in tiptop condition.