Very irritated with SMC right now to say the least. I have purchased batteries from them for 2 1/2 years. Have gotten several track locals to make the switch by my recommendation. About 2 months ago I placed an order for 3 4s batteries. At the same time a teammate of mine ordered 2 4s and 2 2s. I have one 4s that one cell on never charged past 3.87 volts after 3 hours of balance charging. My teammate had one the same way and also had a 2s that was the case was busted on it was swollen so bad as soon as we opened it. The 2nd 4s of mine started the same issue with one cell not charging after 2 races. The 3rd 4s of mine now takes forever to balance because of one cell in it. I have yet to contact smc because my partner has sent 8 emails and made 10 telephone calls with no response at all. I was awaiting the outcome of his communication with them before I went thru the same. I guess it will be a waste of time it seems. I can understand having a problem that is out of your control. Likely seems a bad batch of cells. What i can't understand is ignoring someone who is directly linked to probably well over $1000 dollars of battery sales. Fortunately for them, smc's problems with our packs are going away..... Permanently. If there is any change in customer service or resolve to this situation, I will immediately inform you fellow racers.