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.