It is recommended that you store them at 40-50% charged. This is what I do, and it certainly doesn't work for everyone all the time: After I fly a battery, it is discharged to around 15-20%. When I get it home I put it on the charger and set a reminder timer to 25 minutes. After that 25 minutes it is somewhere between 40-60% charged. I leave it that way until I know I am going to fly again, at which time I charge it up to full or near full. Lather, rinse, repeat. I have also thought I was going to fly, charged a battery, then didnt fly, left it that way for a couple three days, then flew, lather, rinse, repeat.
The school says to not let them sit fully charged or empty for long periods. So something in between.
I have also had one battery go bad on me while taking good care of it, same as the other two. Dealer replaced it and other two older ones have been fine so far. 60+ on two, 10 on the other replaced one.
Don't lose sleep over this. Unless you are OCD or **** retentive, just try your best to store them at 50%.
Good grief, put them in the fridge? You have go to be kidding me.