Lots of bad info on this forum. I'm perplexed by how many people are uninformed.
Don't let anybody who has never boondocked other than a Walmart parking lot tell you that a factory 13.8 volt converter is ok for dry camping. IT IS NOT.
A factory 13.8 volt converter is ok if you are plugged into campground power in 24-7, a stock single voltage converter will eventually charge a discharged battery but it will take a LONG TIME. You don't have the luxury of running a generator for days to charge 2 Group 27 batteries that went down to 40-50% capacity with heater running all night. A single voltage charger is ok if you camp at campgrounds with power. IT NOT RECOMMENDED if you intend to boondock/dry camp and run the generator as little as possible.
Progessive Dynamics has a battery charge time chart showing charge times of a 125 amp hour battery at different voltages with a battery fully discharged Here is a cut and paste of the written discussion:
The Battery Recharge Curves chart shows the amount of time it took a PD9155 (55-amp) converter set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.
14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.
13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.
13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge.
Charge Wizard RV Battery Charging
Running a 13.8 volt single voltage charger SIMPLY WILL NOT WORK for dry camping. Please don't listen to those armchair quarterbacks who have never camped more than 5 feet away from a 30 amp service panel.
Minimal charger (converter) size should be 1/5 of amperage capacity of your battery bank. I have 400 amp-hrs of battery capacity in my camper and have an 80 amp charger (converter). A little extra capacity wouldn't hurt so you have residual capacity to run the camper's 12v items such as lighting, fan etc..etc..
Generator size-GET A LARGER ONE THAN YOU THINK YOU'LL NEED OR YOU'LL BE SORRY.
(a) If you have a 70 amp charger (converter), you'll need at least 900 watts or more to run that charger (converter) because a charger/converter is not 100% efficient. 70 amp x 12 volts = 840 watts out of the converter but you may probably need 900 or more watts from the generator to get this output from the charger (CONVERTER)
(b) Don't forget that if you only have a 1000 watt generator and your batteries are dead, you may not have any residual generator capacity to power other alternating current items in your camper. Want to charge your batteries using a 70 amp converter, run coffee maker, TV, stereo, etc...etc.. you may be SOL (short on luck).
(c) Don't forget altitude. Planning on camping in Colorado? I camp at 10,000 feet usually and I lose 30% generator capacity at this altitude (3% loss in engine output for every 1000 foot gain in elevation).
Simple rule of thumb is to increase generator capacity by at least 50% of what you think you need. This will cover high altitude camping and give you reserve capacity for when you need it. Read generator labeling very carefully. Many 3000 watt generators are actually much less in continuous output. My generator, has 3000 watt output (at sea level) and 3600 surge capacity. A champion 3100 watt inverter generator is really a 2800 watt generator with 3100 surge capacity.
I've been boondock camping for about 10 years in the back country of Colorado. Yes, I have an axle lift on my camper to get to some of the good spots where 4x4 wheel drive is mandatory. I can stretch out 30 gallons of water for 2 adults and make it last 7-10 days. I once had a "2000" watt (actually 1700 watt) generator and quickly realized there were times it was insufficient especially when running it in the morning to recharge the batteries, running coffee maker, while wife fires up her hair dryer....not good.
Solar power is a great option but don't expect solar to completely replace your generator.
3000 watt continuous output Boliy generator
400 amp battery capacity between 2 battery banks (I actually have 3 battery banks but the 3rd bank is only used in an emergency and is separately charged).
400 watts solar with 40 amp MPPT controller
1500 watt pure sine wave inverter with auto-transfer switch (.75 amp/hr idle current draw)
100% LED interior/exterior lighting except for scare lights
Cheap 700 watt backup generator just in case!