Sorry, living in Canada, I went for the first site where I know these things exists....
Those "Powerbox" are used for
1. Camping & RV's where you want to get 110V in the wilderness.
2. Boosting & jumpstarting cars in a Canadian winter.
3. Plugging in power tools at the jobsite.
You can usu. find them at an automotive supply place or a camping/RV store. We have them at most general purpose retailer here (even Walmart has them ... comes in handy at -40 ...
) I know Sears had them as well.
At the end of the camping season, the small ones often go on sale for $150 or so. <You can get smaller ones for less than $100, but they really only store enough charge for 1 single boost.> You won't be able to get a jobsite one for that price ... saw one at HD for like $600.
Search "110V Power Pack" to see if you can find some in the US.
This is an example of one in the US I found <no idea how good they are!>:
110 VAC to 12 VDC Portable Power Supplies / Packs
You might want something like the 600W Duracell one.