I've owned every iPad since the original in 2010 and I've found the air 2 worse than the air which in turn was worse than the 4. I wouldn't rule out a fault with mine, I've wiped it yesterday to test and got the same. I've used it on and off for web browsing between 5 pm and now and it's dropped 32%. I'm also wondering if the light nights and the fact I mainly use it in the conservatory so the auto brightness is mostly at 100% is the problem. I'm sure it wasn't always like this, so maybe it's just that and it will return to normal in the autumn / winter. Either way, it's a smaller battery than the air so some improvement is needed I think in the next model.