It is fine to charge it on the over night charger all night even if you only flew one time the day before. In fact this is usually the best way to charge them if the charger is meant for the battery size being charged. Also may I suggest you get a cycler. Every once in a while you should cycle them to check the capacity. I suggest the accu cycle elite since it can act as a fast charger and can charge glow plug igniters. Just as ggretired said buy a extended volt meter that puts a load on the batteries. If it is 4.8 volts i usually put it on the field charger even though i could squeeze one more flight in.