If your goal is mass production then there's a path from initial
prototype to production, and there isn't really a concept of a "final
prototype". At some point one you think you've got it close enough, you
ideally start talking to a manufacturer (if you're not already doing
that) and you do a small build with them for engineering validation
testing (EVT), which makes sure that all the functionality is there. If
you're happy with that you progress to Design Verification Testing
(DVT), which is a larger build where you're correcting errors but not
making any changes to the feature set. Production Verification Testing
is a large-enough build done on the real production line to check that
all your documentation is correct, that the thing can really be built
and tested and there aren't any bottlenecks or yield issues. Ideally you
sail through this seamlessly because at the end of DVT you should have
it all figured out and any required changes have been made. If you're
satisfied with PVT then you're into production. All three of these
stages repeat until you're satisfied, so you can have EVT1, EVT2, etc,
followed by DVT1, DVT2, and so on.
As for things like the batteries, you need to have a clear, written
specification that states that the operational life on a set of
batteries (or on a full charge if rechargeable) shall be greater than X.
that way they have to pick a battery that meets your spec. If they chose
a cheap one that met the spec but is not as good as the one you chose
then either you agree that they've cost-reduced it so it meets the spec
or decide that the spec was wrong and you want it to last for three
years, not a week. You need a durability and environmental spec too, the
thing will be dropped, suffer impacts, get wet, get left in a hot
vehicle, someone's going to try to bend one, etc. Engage the idiot part
of your brain too, switch off common sense and think of stupid things
that people might do to or with your product. Then shut up the idiot and
turn the common sense back on and marvel at what your product is going
to have to survive before figuring out which idiocies it is
cost-effective to prevent by design and which ones you explicitly
exclude in the warranty.
You do need someone who is on top of things. Students are good at many
things but what they usually don't have is the hard practical
experience. Without relevant guidance and instruction, they are going to
make the same mistakes that those of us who've been around for longer
have made and learned from. The real world is a lot different from
academia. You do need someone with experience of taking a design from
concept to production who can look at things and point out the
weaknesses and suggest improvements and who has the authority to insist
that something is corrected before progressing to the next stage. This
is either something you pay for, or given the end users in your case,
you may find someone who will volunteer some time. Eventually you learn
enough from them that you can be that person.
Oh, and weren't you talking about James Dyson, he's the vacuum guy.
Dave