ugh... That could get expensive all on it's own!!
M&S,
Here is the thing with Batts, they have an internal resistance, so when that starts to rise they dont perform as well, they will still put out 4.2V but it wont last as long and that internal resistance starts to Rise, so keeping like 4-6 in rotation is a good way to use them, you shouldnt take a Batt right out of your mod and slam it right into the charger, or right out of the charger and right into the mod, this is like constant use charging then draining, Resting them in between use and charging is the very best way to run & charge Batts it will keep that internal resistance lower and they will last longer, this is why I say to not only run 2 Batts,,, up to you but what I say is true