A handy way to charge a battery bank when you are free camping is to use a 230V generator. We recommend to the quiet camping models like the Honda EU series (not the industrial building site type ones). The Honda EU models produce a very clean output signal which is suitable very sensitive electronics. Better still, it;'s very quiet. There is a social convention though - don't run a generator outside the hours of 8am-8pm, and if you have close neighbours, ask if they mind first.)
Battery Charging With a Generator
How they work
Most generators have a 12V output built into them however trying to charge a battery using this is almost a waste of time. Charging batteries this way will take many hours and possibly damage your batteries if done often. The 12V output is usually limited to around 8 amps, the voltage can fluctuate and is not suited to effectively charge batteries. You can use the 12V output to partially charge your battery in emergency situations (say your car battery is flat) but keep an eye on your battery for overcharging & excessive gassing.
A better way
Use a Smart Charger (230V – 12V) powered by the generator. A smart charger uses 3 or more stages to charge the battery bank exactly the way it wants to be charged depending on its state. By upsizing the smart charger you can charge the battery at a much faster rate that the generator’s standard built-in unit. Be aware that there is a limit to size of charger you can use on your batteries.
The compromise - generator run time VS battery charge level
Charging batteries up to around 90% is the best compromise if you want to run the generator for as short a time as possible. To charge your battery bank up to 100% full would take considerably longer and really is wasting fuel. It's best to leave the full charging cycle for when you have access to grid power, or you could do it once a week if desired.
Most smart chargers have indicator lights which show which stage the charging process is up to. If you want to stop charging at the 90% level, shut down your generator when your charger reaches the absorption stage. This comes after the boost or bulk mode has finished.
What size do I need?
The bigger the charger, the less time you’ll have to run your generator. Click on the image below to see a comprehensive guide to choose the right one.