Originally Posted by JD Gumby
Why not? Would you actively use your tablet/phone for more than that in a normal day? A device rated at 8 hours for battery life is more than enough for normal usage as long as you're not afraid to plug it in before going to bed or for a heavy task (like streaming a movie to your TV or something), and let the screen sleep when you don't actually need it on.
You'd be okay with adding 50% to, perhaps even doubling, the thickness (most tabs seem to be just under 1cm thick) and greatly increasing the weight? You'd be looking at a bit over 2lbs for a 10" tablet (perhaps even a full kilogram; at which point you might as well get a laptop instead) and probably closing in on 1 & 1/4 lbs (like 675g) for a 7".
You make large false assumption on thickness, and on weight minor error (kg assumption). The current battery takes less than 50% of xy dimensions of (example) toshiba thrive 10.1 or iPad3 and is 0.2 inch (5mm) thick at .4 pound.
New battery double power would spread across entire tablet add only .1 inch and add .4 pound so even heavy thrive at 1.6# would weight 2# total, ipad3 would be 1.44# +.4 # for 1.84# total and .37" +.1+ for .47" or about 12 mm thick.
config of all tablet would change so shape of battery would differ and decrease above calculated thickness.
wgt might decrease with combined battery case