There is no useful, simple answer to this. What is average usage? Two, three, eight hours a day? Even if you collected tons of data about how often most people use their iPads, and how much battery discharge a day, it would only be meaningful to the few people who actually use the iPad at roughly that point. That’s why, even though Apple probably has this data, it doesn’t state something like (your iPad’s battery will last 4.5 years). Because it would end up pissing off all their customers who don’t get what they think is 4.5 years of solid use out of the battery.
So lets run a couple scenarios:
(1) If you use the iPad a lot (almost completely discharge it every day) the battery should still have about 80% of it’s original capacity after three years. If you use it so much that you’re recharging it more than once a day, then less. It’s also iportant to note that the more heavily you use the iPad, the more impact that lost 20% will be. You go from 8 h ours of worry free usage to 8 hours before you are looking for a place to recharge.
(2) If you typically discharge the iPad to 50% each day, the battery should have about 80% after six years. Less, in truth. Aging is also a factor in battery life, and after six years it may be more important than the charge cycle. As before, the impact depends on your usage habits. With amount of useage, you might not even notice you’ve lost some battery capacity.
There are other factors, including the fact that all batteries are not equal. Some will fail early, and some will seem to hang on forever. Here’s Apple’s info page on
Batteries.