When using one of these devices, should the engine of your car be running from time to time or, in other words, will the inverter run your battery down in short order?? How about running the inverter for a long time, say, building a deck at the lake where there is no power and you’ll be using a circular saw, drill, miter saw, etc. for many minutes in a day?? Anybody have experience with one of these things?? I have a generator, but, an 8000 watt generator is a lot more effort to load and transport. I can get an 2000 watt inverter for less than $200.00.
Car batteries are not designed to discharge power over a long period of time. Some people with campers put a deep cycle battery and switched circuit under the hood and, after driving for a few minutes recharges the starting battery, switch alternator power to the deep cycle.
Lets say you used two 6v golf cart batteries, with 520 amp hours. 520a x 12v = 5300 watts. Your circular saw probably runs at 10 amps, with a surge of 15a; 10 x 120v =1200 watts. On paper, these batteries could run the saw for three or four hours solid without charging.
Check the efficiency rating on the inverter. I use a Trace inverter for household power that runs at 95% efficiency, but there used to be inverters running at 70% efficiency (so I have been told by the local ‘genius’).