You'd need to know how many amp hours (Ah) or reserve minutes (RC or RM) your battery can sustain. There will be a label on your car's battery that will say something to the effect of 75-Ah or xx-RC. These ratings are essentially one in the same.
Reserve capacity states how many minutes a battery can have 25 amps drawn upon it before dropping to a voltage of 10.5 volts.
The Amp Hour rating tells you how many amps are available when a load discharges your battery evenly over a 20 hour period.
Example: A car battery that has a rating of 75Ah, dividing by 20 = 3.75. This battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts.
Conversely, if your car's battery had a 75Ah rating, and this inverter draws 75 amps fully loaded, your battery will last only 1 hour.
You can calculate this yourself by finding your battery Ah rating and diving by the loaded current draw of the inverter. Example: 75Ah/75Amps=1 hour OR 75Ah/100Amps=45 minutes
Sorry this post was a little drawn out and probably a little confusing, I tried to make it simple, and I hope it helped you out.
answered 6 years, 6 months ago