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Not sure if I trust Phil's words or the Apple Specs site. I highly doubt it'd only be 3/10ths of a mm thicker, that would be so negligible that the battery increase wouldn't compensate for the retina.

.3mm x the length of the length of the ipad is considerably more battery.
 
Hell yeah! Selling my iPad 4 to get the retina mini. Powerful,great screen, and perfect size. Now I can take my mini with me.
 
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