The weblinks that AStravelers posted is a must read for folks who do not understand that there are two types of electricity on an RV, 12 volts DV and 120 volts AC. Understanding how things work is very important especially when trouble shooting. For example, an RV type fridge uses heat to circulate an ammonia/hydrogen mixture to cool the inside of a fridge. THe fridge heater is provided by either a 120 volt AC heating element (uses about 250-300 watts) or a propane flame. However, the control board for the fridge is powered by 12 volts DC. Hot water heater also has a 12 volt DC control board and is run either by propane or a 120 volt AC heating element. Lights in an RV are typically 12 volts DC. Your propane furnace uses 12 volts for the control board, thermostat, and forced air fan. In cold climates, a heater can fully deplete a single group 27 battery overnight.
An inverter transforms 12 volts DC to 120 volts AC but unless you have a generator or solar, running microwave via inverted battery power will deplete them in no time.
A generator or another source of power, e.g. solar power large battery banks is a must for extended boondocking.
Not sure of the link taks about power and how that relates to battery capacity if you are using an inverter. Here is what helps me.
Watts: How much energy a device uses regardless of voltage. Watts is equal to voltage multiplied by current in amps. So, if I have a 12 volt light that uses 1 amp, I am using 12 watts per an hour. A 1200 watt microwave that runs on 120 volts AC uses 10 amps of current at that voltage. Here is where it gets interesting. A typical rule of thumb assuming 100% inverter efficiency (not true as most are about 85-90% efficient) is if you wish to run a 120 volt AC item off of invertered battery power, you need to multiply the 120 volt AC current draw by 10 to estimate current draw at 12 volts DC. For example, my microwave draws 10 amps of current at 120 volts AC. When running my microwave via the inverter, it draws 100 amps/hour when it is in use (at full power) from the battery (that is quite a bit of current by the way). A typical cheapo Group 27 RV battery has anywhere from 75 to 100 amp hour capacity (won't discuss that the higher the current rate, the lower the lower the available capacity as that is another topic). Given you do not wish to draw the battery below 50% of its capacity as a rule of thumb to extend its lifespan, you have, at best 30 minutes of microwave run time before the battery goes below 50% (probably closer to 20 to 25 minutes based in inverter efficiency not being 100%).
Electricity is best understood by relating it to water:
Current (amps/hour) is the same as water flow as in gallons per hour
Voltage in volts is the same as water pressure
Watts is how much water you used. If you run the faucet at 2 gallons per minute for 5 minutes you would have used 10 gallons. The same goes for current.
Good luck and I see a generator in your future and I highly recommend a Champion inverter generator with remote control/battery start. You don't want to run out in your PJ's in cold and/or rainy weather first thing in morning to start your generator to make your cup of coffee. Solar is expensive and not practical for the occasional boondocker but that didn't prevent me from installing a system myself that would have cost me 6500 if i hired a "pro".