nuebattery. Highly recommeded. fast usb charge, and can disable low battery flight mode.
with that it will keep bt & phone on unil the battery is fully dead, not turn it off @ 10%, because what's the point of having 10% battery if you can't talk. ;p
it seems to me that the last 10% last as long as the top 30%
also have you tried nueDynamic clock? it's still got some kinks, but you can always just use it to manually turn down the clock when you know your going to be stuck on the phone awhile. less clock speed, uses less power, and keeps the temps down so charging can continue.