If you're serious about power management, you must hunker down and do some basic math. It's not difficult math, but this calculator will help you and give you confidence.
https://www.rapidtables.com/calc/ele...alculator.html
There's one rule with the calculator: always use 12 volts. When boondocking, your ultimate power source is your 12 volt battery bank. After that, the watts or amps are what they are.
Next: know your battery bank. What do you have? Let's assume 4 x 6 volt Trojan 6 volt golf cart batteries wired in series/parallel to make 12 volts.
Each battery will be rated around 225 amp hours at 6 volts. Two of these in series will be 225 amp hours at 12 volts. Chaining two 6 volts in series does NOT double the amp hours, it doubles the voltage.
Now add the second pair in parallel with the first pair, and you have 450 amp hours at 12 volts.
YOU GET TO USE ABOUT HALF. So your battery bank delivers 225 USABLE amp hours before requiring a recharge.
Now your loads.
Let's assume:
~ Fridge at 500 watts and 30% duty cycle (runs about 1/3 of the time)
That's 41.6 amps per hour x 24 hours x .3 (duty cycle) = 299.5 amp hours consumed per day. Suddenly that mondo battery bank ain't so much.
~ Now lets remember all the other loads: Furnace, Water Pump, Lights, Parasitic Loads from the CO detector, LED displays on entertainment systems, and, and, and. And let's not forget that the inverter feeding your fridge is not 100% efficient. Add in 5% loss for that inefficiency.
Gonna run the TV? Do the math.
Your fridge may not consume that much power. Great. But whatever it does consume...the watts or amps combined with how much it runs...demands a certain number of amp hours. And your battery bank delivers just so many usable amp hours.
One more run at it. Let's assume your fridge consumes 300 watts and only runs 20% of the time....a 20% duty cycle.
300 watts at 12 volts = 25 amps x 24 hours x .2 duty cycle = 120 amp hours out of the 225 usable in your battery bank. You're not sucking wind, but 100 amp hours ain't a lot to do all the other stuff. Hell, your furnace will use about 10 amps, and in cold weather might run 20% of the time. Your water pump uses about 8 amps every time you turn on the faucet. You get the picture.
Use the calculator and do the math.
Meanwhile, if this is a rare occurence (boondocking), prepare to listen to the drone of the generator for extended periods. If you plan to do this often, consider:
~ RV fridges run on propane for a reason. 2 x 5 gallon tanks of propane contain something like 100 times the energy of your 4x6 volt battery bank. Residential fridges are a poor match for boondocking.
~ Consider solar. A 4 x 100 watt solar panel array can produce 100 or more amp hours of charge per day in reasonably sunny conditions. (I have solar on my rig, and I can boondock essentially forever without using the generator except to power 120 volt appliances like my microwave briefly.
~ Use power frugally. Forget the TV, stereo, tons of lights.
~ Batteries suck as power storage devices. As I mentioned, 10 gallons of propane contain about 100 times the energy of 4 x 6 volt golf cart batteries.
When boondocking on 12 volts, there's no free lunch...no magical way to make a battery bank behave like the grid. It's a very different type of camping from RV parks, and to do it well, one must begin with a rig that's equipped for the job. A residential fridge is a really bad choice for boondocking...and a fabulous choice when you have shore power. But for the occasional venture into the boonies, bring plenty of gasoline to run your generator for hours on end and/or add LOTS of solar capacity on the roof.
Above all, don't abuse your batteries. If you drain them dead before recharging, you'll ruin them pretty quickly. Be pro-active and keep them charged. When you fire up the genny and plug in, your converter cooling fan will run during heavy charging. Once the fan goes off, they are not topped off - not by a long shot - but that is a good indicator that they are charged enough to get you through the night.
Use the genny to charge twice a day. First thing in the morning for 3 or 4 hours at least until the converter fan shuts off. Then again for about 3 or 4 hours in the evening (before quiet hours) so that the converter fan has been off for a while. If you want to watch TV, do it while the genny is running.
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