In my experience power inverters are great for powering small stuff like cell phone chargers and laptops. To power a DeWalt 849 polisher you would need an inverter that can handle 1000 watts. An 8 amp load at 120 volts equals 100 amps at 12 volts, not including the loss from the inverter itself. Figure a 15% loss from the inverter itself, so your 12 volt system needs to put out 115 amps at 12 volts. The only place where big inverters make sense is in yachts where you're running stuff like refrigerators, and you have plenty of space to permanently mount big, heavy duty inverters. I would suggest a portable generator to power your polisher.