If i make the base about 3mm thicker then the N900 base, i should be able to fit one of the cells i use for my e-bikes, these a LiPo battery's with only 1C (2C max) and that is for capacity, they do weigh 156g last i checked so it will be a bit heavy, phone has to be 5"+ to fit this but will enable the phone to have 10,000mAh, so usage time should be very good even under very heavy loads, when remembering back to the 3000mAh in the N900 this will be quite an upgrade.

On Speaker "design" im thinking about a release mechanism to let them "flip" out from the sides to be front facing when needed and side facing in normal usage so you can still use the keyboard, after they have been flipped out you have to click them back in, maybe this will change...., you still have to turn them on, this again puts power to 2x3W AMP and shorts jack_detect so all sound is going to amp, else when off the Android phones internal speaker is used - But this might also be subject to change, im always thinking about power efficiency and will have to do more tests on power usage of the amplifier to say if the power hit is very little, will make a hell of an alarm clock with this speaker system

EDIT: 1C rating means this battery will handle a 10A load (37W), so high power flashlight and much more is also a possibility, will do 20A for shorter time