I think a general rule of thumb with our
batteries is around 300 charges before performance starts to drop. I'm sure there's many factors involved in that, someone who knows more than me will have to provide more info.
I assume the drop in performance has to do with internal resistance of the battery increasing as it ages. I have a few 18650s that are well over a year old that have been charged hundreds of times. They still work fine, but don't give as much oomph on a full charge as my newer ones and they need to be recharged sooner.
It's important that the
batteries don't get discharged too much, below 3.3 volts is bad, and that they don't get charged above 4.2 volts. Either will greatly shorten the life span. When a battery has noticable drop in performance or won't charge to 4.2 volts it's time to recycle them. I'm guessing some factors involved is how fast they are charged, how old they are and what charge they are stored at, the brand of the battery.. etc.