iPad 3 run significantly warmer compare with iPad 2, I repeat iPad 2. iPad 4 has exactly same battery as iPad 3, it takes lesser time to charge because of that 12W charger, but that just reduced the charge time around 40 minutes.
That's being said, iPad 3 does offer similar battery performance with iPad 2.
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You are the one being hilarious. What is the point for iPad mini? Really, think about that? If you were to make a iPad mini not substantially lighter than iPad 3, then what is the point to make it?
The whole purpose for iPad mini is light weighted, cheaper iPad. If you were to put same pixel into smaller display, you are not only required to have better processor, at least same amount of memory and larger battery? If you keep the same battery, same processor, same memory used on iPad mini, then change to retina display, what will you get? For sure, the performance will be sluggish, battery life would be terrible.