Billy... you need ~500w x 2 hours = 83 Amp Hours.
To be best, you need 3 hours, or 125 Amp Hours.
A full size, lead acid (wet) battery, on the large end, such as for Semi's or Caterpillar would do it. They are 10" x 10" x 20" and weigh 132 pounds.
You need one of "8D" capacity.
There's not a price here ( I don't think, I didn't read it all ):
http://www.cat.com/cda/files/192183/7/PEHJ0073.pdf
But I'll bet they cost 4-digits ( $1,000 )
Or, you could put 3 regular car batteries in a row, in PARALLEL.
Parallel means you wire PLUS to PLUS to PLUS to device, and
NEGATIVE to NEGATIVE to NEGATIVE to device.
With 3 car batteries, you will be close to 100 pounds, but hey, you can get 3 for under $300.
Now that I think about it, 4 in a row might be better....
I just don't think it is worth it....

The Cost-Danger-Work to Benefit ratio is not good.
Do this:
Take 200 or 300 feet of extension cords ( $60? ) ( 20 pounds? ) with you where ever you go. Take them in 50 foot sections. I think you'll be able to find a plug in 99% of the places you go.
This is why 120 VAC plug-in hybrids are so much more attractive than the EV-1, which pretty much had to be at home to charge, since the charger was large, and specialized. ( And higher voltage ) You are rarely more than a couple hundred feet from a standard plug.
I plug mine in at work for what it's worth. 2.5 hours = 10 cents of power.
*( In rural America... in larger Cities it may cost 20 cents )
I make up for it by turning the lights off during lunch.

-John