The secret: Just do it. They're designed for that.
Nearly all power tools use a "universal" brushmotor that doesn't care if it gets AC or DC.
All you have to do is put 4 or more 12volt batteries in series and plug your tool in. I usually like to run my tools on about 70 volts DC (five batteries). They're a lot quieter that way and still have enough power.
If you want more power, just add more batteries. I think the gearbox of a circlesaw chatters less when it's running on DC. The batteries don't need to be nearly as healthy as what you'd need to power the same tools through an inverter.
Warning: All the warnings about tools, batteries, and electricity apply. If you want to get hurt you'll find a way, just like you would have without all this expert guidance.
Here I'm using a totally motley assortment of scrap batteries wired in series with my car battery.
If you have mismatched batteries the weak one will discharge first and need to be removed.
A lead acid battery is dead at 10.5 or 11 volts. Recharge then or it could stay dead.
You'll have to monitor them with a multimeter and write on the batteries with a sharpie so you remember what to expect.
I'm using one or more wimpy radioshack alligator clip cables, which make a decent fuse.
Don't try to put your solarpanels in series with your batteries for extra voltage. They can't deliver the starting current your motor needs. When the motor stalls that puts the whole series voltage across the solar panel which can be bad. The same effect means you want to take the weak battery out of the series as soon as the tool starts feeling weak.
To learn more about the junk battery powertool lifestyle, see the next Step.
Step 1: Happiness
Here's my workshop. I'm at a free campground in the Everglades getting ready for a trip into the swamp. It's winter, which is the dry season. So it's 68 degrees and sunny most days. The pond is full of fish and alligators. Some of the alligators have been fed by people, which adds excitement to the situation.
Find free campgrounds with the Free Campground Directory.
My sun awning here is a mirrored "survival blanket" over a camo tarp. Don't bother with that, just get a real opaque silver tarp from CampingWorld. Home Depot, Lowes, etc. only carry the fake ones that make a solar oven that costs as much and won't prevent sunburn.
I do my cooking in a pressure cooker over a hobo stove. I don't have to watch the food cuz it won't burn before the fire dies down. I boil a dozen eggs or some fish stew on the bottom while I steam-bake a big bagel from my own dough in a stainless bowl floating ontop that. I grow my own sprouts for vegetables or eat the herbs that locals show me. So I don't need groceries and can stay away from towns a long time.
Every couple of days I'll drive a couple of miles til I have cell coverage and check my email to see if my life is still simple. I use my cellphone as a USB modem. My service is an old plan from Tmobile with a Motorola V188 phone. If I've been doing a lot of woodwork I'll gang up my batteries to recharge in parallel during the drive.
I sit in my comfy recliner in the shade and make cad drawings of Indonesian sailing canoes on my laptop. Solar panels charge my assortment of desulphated scrap batteries using bundles of christmastree lightbulbs as current regulators. I sip sun tea and nibble sprouts and a bagel with fish stew.
Colorful characters see my low-stress setup and come greet me like a long lost friend. They offer me beer and before long they're teaching me how to tune a spritsail like they did growing up in a Jamaican fishing village, or telling me what it was like to be imprisoned in "The Tombs" ("No privacy man! The worst!").
Step 2: Universal Motors
This concept of running power tools on batteries, AC, or whatever source of electricity you've got is nothing new. Back in the day a lot of truck alternators had a high voltage DC output for powering tools.
Even now you can trick some alternators into putting out 110 volts DC by putting more current into the field winding. They never got around to changing the architecture of the alternator.
But you better disconnect it from your truck's electronics and batteries first.
Here's the motor plate on my Skil 100 planer. It says "Volts 115 AC-DC".
It doesn't care what flavor of juice it drinks as long as it's pressurized to around 100 volts.
This much-loved power tool was made almost unchanged from the 1930s til the 1980s.
Like most power tools, it has a universal brushmotor.
Once they they got the bugs out and got set up to make these motors in large volumes, the tool makers never got around to adding anything that that would make the motors incompatible with DC.
Some drills have a speed control that won't work on DC. Usually the drill will spin just fine, but only at full speed.