The more weight and circuitry there is, the higher the current consumption will be.
During the build and test phase I will use a generic power supply with current measurement. This will help choosing the batteries.
In the first test phase the current measurement with rolling motors is about 1.5A, this give me an estimation of a 2-2.5A when finished. If that value is too high, the result will be in a longer run time: which is not bad.
With a consumption rate of 70%, two 2500mAh batteries in parallel and a 2.5A consumption, the battery life is around 1.5h. Considering that the motors will not run all the time an estimation of 2h looks good.
What kind of batteries? And what about the voltage?
First off, the voltage. It should be over 7.5V in order to power up some BECs (Battery Eliminatior Circuit). In my idea there will be 3 of those with a rated 5V/5A maximum output. One for the Raspberry Pi, one for the ECUs and one to power up the arm.
In this case, the four motors run at 9V, thus a 9.6V battery works fine.
There are many kind of batteries available. On the first build of Botler 1 I will use NiMH. LiPo have many advantages but are too dangerous.