If you mean how many years the battery will last, it depends on how much you drain it down each day. Apple says it should still have 80% of it's capacity after 1,000 full cycles, so if you used up 50% each day and recharged each night, that's a half cycle and after 2,000 days your battery still should be decent, though aging.
YMMV, of course,
And it does seem to be important to thoroughly drain and recharge once a month for calibration.
I find my iPad drops roughly 8 percent per hour in normal use - I hardly ever watch videos.