I think he's over-estimated the cost of batteries. I'm pretty sure you could get 55Ah 12V lead acid batteries for about 1/2 that. This is relatively common for people running off of solar power.

After some further investigation, I discovered that my calculation exactly matches the upper bound stated by the National Renewable Energy Lab's estimates on cost, "$200/kWh"

http://www.nrel.gov/docs/fy02osti/31689.pdf

But yes it looks like you can also manage about half that cost for a similar system (their stated range is $80-$200 per kWh).

That's significantly more expensive though.

A 5KW gasoline generator is $500 new, significantly less used and definitely much more reliable than car batteries. It would also probably out last them. And it requires practically not maintenance whereas most car batteries that aren't in use would die without constant maintenance.

I think they meant to load-average so they could get away with a 600W generator instead of 5.5kW.