For those who have not purchased an alternate battery charger system and use the stock charger like me, I noticed something today you may note. I was charging a couple of batteries in succession after flying; I did not give the charger any cooling off in-between batteries. After the completion of one battery successfully I put in another and walked away a bit. I heard the charger signal report and returned to see the "blue light special" indicating that there was a charging error. I tried it again and could not get rid of the default, even trying another battery which was in a storage mode. It turned out to be the charger itself had become so warm it would not allow any further activity. After cooling it worked fine. So be aware that successive batteries being charged, even once cooled down themselves from flying may meet resistance from the charger itself if it is too warm.