Got a protek 620 charger. Problem is all 3 of my lipos only charge to 4.19. On each cell. But days 8.40 volts

I have found that some batteries will go up to 4.20 and others will stop at 4.19 and in rare cases even lower. Depending on the temp, sometimes the same pack will end at 4.19 or 4.20. My guess from wathcing the charger at the end of a charge is that the chargers I have used will try and balance the pack at 4.20, but if after some time a cell will not reach that goal it will settle both at the best it can do. The reason this can change with temp is because the internal resistance changes slightly with temp.

My older "cheap" chargers would often end with one cell at 4.20 and the other at 4.19, or even one at 4.20 and the other at 4.18, when I was charging an older pack with a weak cell. Since switching to a charger with a stronger balancer I have not seen this, but a pack with a weak cell may still "peak" at 4.18 or 4.19, rather than 4.20V.

I do not believe this is a cause for concern until you start seeing a difference of 0.05V or more between cells. As for the difference in the main port and the balance port voltages, I believe this is because the power output wires and connector have lower resistance than the balance connection.

If I charge at 5 amps the go to 4.20 each but if I charge at 10 amps they stop at 4.19 each.

Quality chargers can be adjusted/compensated for this.

Yes they can but at the same time I would verify your voltage with a quality volt meter and adjust your settings accordingly. Just to make sure. And if by chance you go to a ROAR race, getting busted in the tech line because your charge settings are a little off would be no fun.

I know you know all this Andy, just an fyi for others.

pro tek 620 dont seem to have that option.