Originally Posted by powerwagon60
Keep in mind 1000watts ac pulls 100ahrs from the batteries heavy loads from battery will not last long
This is not exactly correct. Watts = Volts x Amps
1000 Watts at 120 Volts equals 8.3 amps (1000/120=8.3)
1000 Watts at 12 Volts equals 83.3 amps (1000/12=83.3)
If your microwave (or whatever) pulls 1000 watts while in use, then it is pulling 8.3 amps of AC power or 83.3 amps of DC power through an inverter. It will only pull this amount of power for the time it is running.
A 100 amp hour battery can discharge 100 amps continuously for an hour (in theory). Batteries are really rated based on a 20 hour rate so realistically it won't be able to supply 100 amps continuously for an hour. It gets its 100 amp hour rate by being able to discharge 5 amps continuously for 20 hours. The Peukert effect says the battery will last less than an hour if discharged at a rate of 100 amps, but this is getting way to technical.
In the RV world, you will rarely see sustained (hour long or more) heavy amperage draws from a battery (unless you are trying to power an AC unit, which while possible is not practical with standard batteries). Fifty percent of the battery's rating is actually usable so you can get 50 amps from this battery.
In the above example, you could run that microwave for over half an hour before your battery discharged to the fifty percent mark (50/83.3=0.60). 0.60 of an hour is 36.6 minutes (0.60x60 minutes =36.6). Of course there is some overhead in the inverter and line loss in the wiring that has to be factored in (along with the Peukert effect) so it would actually be a little less than this.
I can't think of the last time I microwaved anything for more than 3 or 4 minutes, so you could do that up to six times before the battery was drained in this example. Of course if you are running a larger inverter, you probably have more than a measly 100 amp hours of battery available to it. This will also increase what you can run and how long you can run it for.
I agree that you need a good method of recharging your batteries if you plan to run heavy loads on an inverter. Solar is an excellent charging source and should be a part of a well rounded boondocking power solution (or at a minimum a good generator).
I probably geeked out a little and got way too technical in this response, but hopefully it will be worthwhile to someone.