The quickest 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 or the Yamaha EF series (not the industrial building site type ones. There is a social convention; don't run a generator outside the hours of 8am-8pm, if you have close neighbours, ask if they mind first.)

Most generators have a 12V output built into them however trying to charge a battery using it is almost a waste of time.

Charging batteries this way will take many hours and possible damage your batteires if often done.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 to charge your batteries is to connect a Smart Charger (230V – 12V) to 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.

What size charger do I need?

The below list shows a few CTEK charger models and the battery banks size range they are suited for. The bigger the charger, the less time you’ll have to run your generator for.

CTEK XS7000 (12V, 20-100AH)
CTEK XS15000 / M200 (12V, 60-225 AH)
CTEK XS25000 / M300 (12V, 60-500AH)
CTEK XS14000 (24V, 60-225AH)

Charging batteries up to around 90% is the best compromise

Charging batteries up to around 90% is the best compromise if you what 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.

The CTEK 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.