They have a nominal voltage of 3.7V or 3.6V. They are charged at 4.2V, and disconnected when the charger says 4.0V. Does that mean they are 3.6V when they are empty, or are they overchaged when they are 4.0V? How low in voltage can they go and still have plenty of current? Thanks. I'm designing a 36V lithium ion battery made from commercial 3.6V cells, since commercial 36V batteries are so expensive.