Spent quite a bit of time today speaking to Battery dist. & manfs and all agree that you are not going to get much more than 1300mAh out of a battery that has to be no bigger than 65mm x 38mm as it fits in a recess in the circuit board. Prob can be up to 8mm thick.

As far as I can tell all the batteries that are 1500mAh or more suddenly increase in size as it stands at the moment, what it will be like in another 4 years when I need to replace this one again? hopefully technology will have moved on again in batteries and hardware :-)