A while back there was a little discussion that involved why we do not
run air conditioners when we are not connected to 120 (or 240) VAC land
line.
If everything was 100% efficient, it would take 10 times as much current
at 12V as at 120V. For example, my 13,500 Btu A/C draws 16 amps running
at 115VAC. For this to be operated from the batteries thru a 100%
efficient inverter it would draw 154 amps from the batteries.
This is bad enough, but in reality it's much worse. Inverters are not
anything close to 100% efficient. According to
DEEP CYCLE BATTERY FAQs 4.4, by Bill Darden, at
www.uuhome.de/william.darden/dcfaq4.htm,
"A common application in recreational vehicles is using a DC to AC
inverter, which is used to convert 12 VDC to 120 (or 240) VAC power. It
takes between 12 and 14 amps of 12-volt DC power to make one amp of 120
VAC power (or one-half amp of 240 VAC power), so large deep cycle
batteries are normally used with inverters."
The only practical way to run an A/C when not connected to land power is
by a generator.
Al Grayson