I have one battery (Reaction 2s 5000) that charges fine and balances out to 4.20 on each cell. I put the batteries on the charger (Hitec X2) and put in Lipo storage mode. When the battery starts to discharge the cell count flex's back and forth between .02 - .03 difference between the cells when discharging. The battery is in a hard case and doesn't feel any different than the other 2 that I have. (doesn't feel like is swollen / puffed)

Should I be concerned?

You are fine. As long as its balancing while charging is the most important.

Thanks for the help. When charging the cells are off by .02-.03 and when discharging the most is .05. Typically when discharging off .02-.03. At the end of the discharge or charge cycle they are both the same. Just wanted to confirm. After seeing a couple lipo fires at the track it's got me on edge.

what were the circumstances of the fires? I am in several RC flying clubs and there are a huge number of Lipo batteries being charged and used on any given day. I have yet to see a fire caused by charging . From what I have seen, fires are only when a plane crashes and the battery gets broken open so the stuff inside gets exposed to air.

As batteries age, they won't balance as well, won't hold 4.2V/cell when fully charged, and the IR will get worse. Those things won't usually cause a fire. At some point, it becomes time to retire a battery. I have a pair of 6S 5000 that I use in 550-size helicopter. They are about 4 years old. Last time I used them , the were quite hot after a flight; still working but I decided it was time to put them out of their misery but they did fail and cause a crash.