The Internet is full of articles which has description of kinds of testing, including a those where non-functional testing. However it become to hard to find a proper one, especially if we’re talking about a industry-specified devices based on common mobile OS. This kind of devices designed to be serving to specified software for the work on field. Yet it boring to read huge amount of plain text. Thank God, we have such a great tool like Mind Maps, a graphical representation of our thoughts.
Look at the mind map below (which I created using free version of XMind, but there’s plenty of alternatives), it represents (I believe) all kinds of non-functional tests that could be conducted over some Sales App+HW (Android phone+Printer+Payment Terminal) bundle. Click on the picture to see it in the full size.