This has been asked before, and answered with a link to Apple's page
where they recommend keeping it fully charged most of the time but
once a month letting it run almost all the way out.
Letting it run out occasionally "recalibrates" the components that
tell you how much time you have left.
But each battery model has a predicted life of some many charge cycles.
If you run it all the way out and recharge it every day, you use
365 charge cycles in a year. If it is rated for one thousand, then
you'd have to replace it in three years.
Holly on Holiday