Our rig has a few choices for power. The engine has it's own battery just like the one in your car. It's charged by the alternator when you drive and is used to start the engine and power the vehicle lights if the engine isn't running. The difference with our rig is that it can also get charged if the rig is connected to the 110 volt power supply in a campground.
DANGER< DANGER, WILL ROGERS!!
<Since writing this we had a battery episode and it turns out that the chassis battery DOES NOT GET CHARGED ON SHORE POWER> (at least on our particular rig it doesn't)
Also if for some reason the battery for the engine (Called the Chassis Battery in RV's) is dead then there is a switch on the dash that makes the battery that powers the rest of the rig (The Coach or House Battery) switch over to power the engine to start the engine. The coach battery or batteries are separate from the chassis batteries (our has 2 but some rigs have 6 or 8). On our rig the coach batteries are by the generator and the chassis battery is in the engine compartment similar to a car. The engine alternator will also charge the coach batteries while you drive along.
All this naturally is 12 volt. Our coach batteries will provide basic lighting and the power for the controls to the fridge and water heater. It won't power the microwave, TV, VCR A/C or any of the outlets around the coach all of which need 110 volt.
So where does the 110 volt come from?
Our rig has a generator that runs on gas, it's under the rig in it's own compartment. If there is nowhere to plug the rig into then the generator will provide enough power for the accessories mentioned above, plus it will simultaneously charge up first the chassis battery and when that is fully charged it will switch to charging the coach batteries. This way if you are boon docking for an extended period you can fire up the generator and put enough charge in the batteries for the evening. Naturally you could run the generator at night too but it's considered rude to do so as the generator is fairly noisy and can spoil other camper's enjoyment. If you are somewhere hot you can run the A/C system to cool down while on the generator. Our rig can run the 2 A/C's at the same time on generator power. That is very nice but you can't run everything at the same time as the generator produces a limited amount of power and if too many things are turned on at the same time then a breaker will pop.
ATTENTION ATTENTION WILL ROGERS.
Another discovery we have made (the hard way) is that the generator draws fuel from the RV gas tank. As a safety measure the generator won't draw fuel of the tank is below 1/4 full. That way you can't run your main tank dry using the generator and leave yourself stranded. So if your generator suddenly stops check your fuel gauge.
If you have partial or full hookups at a campground then you can plug the rig in and use 110 volt power without the generator. Campgrounds have "Pedestals", one for each site (Hopefully) usually they are next to the water faucet and the sewer connection and on the left side of the vehicle which is where RV's are set up for hook ups.
At the pedestal, We are plugged in to the 30 amp outlet. The one on the right is a 50 amp outlet. The box hanging down is the surge protector.
Older and smaller rigs have a 30 amp service. That means that you have a maximum of 30 amps of 110 volt current available. In effect that usually means you could run 1 A/C unit and maybe the the microwave, but if you try to turn on a second A/C or the toaster then a circuit breaker will pop and spoil the fun. So you have to be aware of what you are running.
Big modern rigs have 50 amp service so you can run more stuff but there is still a limit. The plugs and sockets for 30 amp and 50 amp services are different and so a 50 amp plug won't fit in a 30 amp socket and vice versa. You can buy adapters that will let you use them together but it won't let you use 50 amps in a 30 amp rig because the wiring and breaker panels are still sized for 30 amp. Conversely you can plug a 50 amp plug with an adapter into a 30 amp pedestal but you won't be able to get more than 30 amps and the breaker on the pedestal will trip if you try. You can also get an adapter that will let you plug unto a household outlet. This is good if you want to charge the batteries at home but there isn't enough energy to power much more than the TV
The electrical systems on a rig are pretty smart. In our rig if we are plugged into a pedestal and start the generator the system will isolate the pedestal power and just use the generator power to avoid voltage issues. While all this is happening the rig is happily charging the coach batteries too.
So all is well in the electrical department right? Wrong!
Campgrounds have a nasty reputation for poor power supplies. Due to the large number of rigs plugged in to the supply the voltage can drop below 110 v, thunderstorms etc can cause voltage spikes. Some pedestals can get damaged or were improperly wired by the campground handyman. All of these can and will damage the very expensive electrical and electronic equipment in your rig. Luckily there are testers, surge protectors and low voltage protection devices available. The one in the picture above has a test function built in so I plug that into the pedestal first, turn on the breaker and look to make sure I have a green and 1 red light. If not I don't plug the rig in. Always do this before hooking up the sewer and water because an incorrectly wired pedestal can cause electric shocks. If it's not right find a site that's wired properly. If everything looks good I turn the breaker back off, plug the electrical cord from the rig into the surge protector and turn the breaker back on. Knowing what I know now if I was buying a surge protector for the first time I'd buy one with low voltage protection. Low voltage can be just as harmful as a spike but low voltage is much more common
To complicate things a little, all the lights in the rig are 12 volt even when the rig is plugged into the pedestal or running on the generator. There is a transformer that takes care of that. Also the controls for the fridge, A/C and water heater require 12 volts even though the water heater runs on propane and the fridge is just a wonderful thing that can run on propane, 110 volt or even 12 volt automatically. If you are running one of the A/C units then switching the fridge manually to propane might allow you to run another appliance on 110 volt without tripping the breaker. Perhaps.
Some people who do a lot of boon docking add solar panels and voltage controllers/smart chargers that recharge multiple batteries. They then run Inverters that convert the 12 volt battery power to 110 volt AC power which can in turn power the TV, A/C fridge on AC power and whatever else they want until the sun goes down and the batteries die. There is a whole other subculture of solar power and power converter fans that talk a different language than the rest of us and know what "Power Density" is and why it's important.
So now you get it right?
If you do then write it down and tell me because I'm still learning....