I am no Lipo battery expert by a long shot but I figure since I am learning about electric power and see a question I am not sure about, I need to know the answer also
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If you are talking about batteries which have been
balance charged ( do you know that not all charge options balance the cells ?, not everyone does... ), I can tell you that most of my Lipos ( totaling about a dozen at the moment ), see a final voltage difference between cells of no more than 0.001 V ( after balance charging ). I have one battery that has a 0.005 V difference.
I then did some reading to get other people's ideas ( because I am interested too ), and found that previous respondents to a question like yours ( and they have thousands of posts to their names, for what it's worth ) generally gave the figure for max. V difference between cells after balance charging as 0.02 V ( 0.03 V and 0.04 V were also mentioned ). These people seem to have been using their batteries without issue with their given values.
Bear in mind there may also be inaccuracies in the voltage measuring equipment and also in the battery charger's balancing function, that could account for some or all of the seen voltage differences between cells. .
I can't really speak as to the implications of higher voltage differences than these, other than possibly reduced battery capacity. ( Incidentally, just be sure you never run a Lipo cell below 3.0 V and for maximum battery life, 3.7 V is not a bad minimum to observe when actually using your packs. I once left a battery in my rc plane and thought it was safe because the switch was off. Nope. There must have been some minute current draw somewhere and over the days the battery cell voltages fell below 1 V. That was an expensive lesson. In retrospect also, that switch on the side of the plane was not in the battery lead path so I should have known better... )