Having a pair of deep cycle 6 volt Golf Cart batteries let's you dry camp for much longer than a single 12 volt deep cycle. Up to 4 times longer. This is simply because there is more lead in the pair of 6 volts. A pair of them weighs about 120 pounds, where a small deep cycle 12 volt weighs about 35 pounds.
One cable connects the two 6 volts to make them a 12 volt, there is no need to change any wiring on your RV or boat or camper to use them. They are similar in length and width to a car battery, but about 2 inches taller and you need two of them, so watch your clearance if they need to fit in a tight cabinet.
The batteries don't care what you charge them with. As in, they just want voltage, it can come from your alternator, a battery charger, a generator, solar, wind, or plugged into shore power using the built in charger/converter.
What they do absolutely care about is the amps they are receiving for that charge.
A pair of Trojan T105's want to be charged at 22.5 amps. Batteries like the 10% rule. They want to be charged at about 10% of their amp hour rating. So a pair of Trojan T-105's rated at 225 amp hours, would like 22.5 amps of charge.
A single Group 24 deep cycle 12 volt is about 80 amp hours, so they would like 8 amps of charge.
First off, ANY charge is better than none. Batteries HATE sitting around. ALL batteries self discharge every month, hooked up or not.
So what is the best way to charge your batteries?
1. The converter/charger built into your motorhome is likely a 30 to 40 amp 3 or 5 stage charger and does a great job of charging them.
Note - If the motorhome is new to you, make sure to check that the converter/charger is working properly before you put it into storage plugged in, so that you won't boil the batteries dry by spring. We can explain how to check this.
2. A 3 or 5 stage battery charger that can do 30 amps.
3. A generator isn't usually a great charger. They will typically say they do something like 8 amps, and really do about 5 amps.
4. An alternator only puts out about 5 to 10% of it's amp rating to the batteries. The rest goes to your wipers, heater, lights, etc. A typical 80 amp alternator would be giving you 4 to 8 amps to your camping battery AFTER it has charged your starting battery. This is a lot of work for your alternator.
5. A 100 watt solar panel through a charge controller will give you 5 amps to the batteries in the bright sun.
So to get the most life out of your batteries, you would go camping, discharge them 50%, charge them back up fully with the 10% rule, THEN put them into storage on a smaller amp trickle charger.
The other methods help you stay out longer between charges, but will NOT give you the best charge for the batteries.
Feel free to ask any and all questions.