Really depends on the tool and your use. My experience with the 18V impact driver is that it needs a top off every few hours, but that's a good time to take a break anyhow. However the Sawzall and chop saw will chew through the biggest batteries in minutes. Fortunately they charge quickly though they are rather expensive. I think they are on par with the Dewalt stuff though I like the Makita tools a bit more. I guess if my jobs were any bigger I'd be using pneumatic tools so I can deal with recharging between tasks.

I've been in plenty of job sites with limited power and heat, and a fresh cup of coffee would be much appreciated. Sometimes you can't make it down to the lunch truck!