Your post reminded me of something. Every one should get a P3 International P4400 Kill A Watt Electricity Usage Monitor.
They are cheap at $17.84 and will help to design daily load calculations. Load calculations also need to take into account charger efficiency, inverter efficiency and generator efficiency. These efficiencies are all cumulative.
Just assume your average gasoline generator converts 16% of energy in a gallon of gasoline to electricity (many cheap units will only do 13%). Available energy in a gallon of gasoline ranges from 114,000 to 125,000 btus. BTUs per watt hour is 3.41 roughly. This gives you: 120,000 X .16 ÷ 3.41 = 5630 watt hours per gallon of gasoline. There are 1800rpm units that attain 19% efficiency and are much more expensive.
Now charger efficiencies need to be taken into account. At best we can use 85% because of numerous different device and charge level factors. This maybe a bit optimistic, but what I have calculated with my Trace Inverters. We now take the 5630 watt hours per gallon of gasoline and multiply it times the the charger efficiency. 5630 X .85 = 4785.5 watts.
Finally we have the inverter losses (or efficiency) to take into account. I chose my inverters for their very high efficiency ratings. Most cheap units will perform much lower. The Trace DR series run about 93% efficient, while many of the cheaper units will do 75%. For calculations I will use the Trace units. We now take the 4785.5 X .93 = 4450 watt hours of useful electricity.
This can be tweaked a bit with inverters that have pass through circuits while charging. You can take you heavy loads, such as laundry and do them during the charging period to bypass the storage and inverter losses. This is how I have been able to approach 5KWH per day critical loads or about 1 gallon of fuel.
I just wanted to throw this out there. These are rough calculations, but will help to understand and plan for fuel storage during power outages. The watt hour meter is also helpful in determining what your critical load usage is. It may be worth the investment for instance in a new higher efficiency refrigerator then storage of more fuel.