Best way to charge battery with free-standing generator??

If you are thinking about solar panels check out these ones www.itechworld.com
They are light weight 100W panels that you can glue to your RV/Van etc and come with a solar charge controller to protect the battery and the solar panels. They are only 3 kg and easier to use then conventional panels.

Your friend needs to see the charging voltage and recommendations of the manufacturer of the battery he buys, before he decides on a means of recharging them. AGM's and voltage recommended to charge, as well as charge rates, vary a lot, from brand to brand.

Get it straight from the horses mouth, not from here, on the internet, none of us warranty your battery, the manufacturer does.

+1 for solar. Otherwise if you must burn gasoline get a 40 amp portable charger.

Get a pair of 100 - 150 watt solar panels, and that will charge them silently without burning any gasoline.

SunElec.com

Fred.

Roy Ken, try impressing 14.8 volts across those batteries and get out your watch :)

If you want to re-charge your battery in a quick three hour time frame then you need to have around 14.4VDC with a DC Current capacity of 17-20AMPS per battery you need to re-charge.

The battery will demand the amount of DC current it needs to re-charge.

Not having enough DC Current capacity in your charge source will still charge your battery but will take many many hours to do it.

Battery Science at work here on how much time it takes to re-charge any deep cycle battery...

The typical BAT CHRG port on the generator is typical unregulated 12VDC source with the capacity of around 6-8AMPS DC Current. 12VDC will not excite the battery enough to do much charge reaction. Battery science says you need around 14.4VDC to start a boost/bulk charge reaction and then the battery will want to demand around 17-20AMPS DC current to re-charge the battery is the quickest time span which will be around three hours of time to return the battery to its 90% charge state or 12-13 hours to return the battery to its 100% charge state...

Everyone seems to think they can come up with their own method and do it better. In the end it just doesn't- At least it doesn't happen with my batteries...

Since the battery demands its DC Current charge level you want to have just the right amount of DC VOLTAGE present to keep the chemical reaction going and not boil out your battery fluids. It seems that the 14.4VDC is where most of the battery manufactures like to use for their batteries. The smart mode chargers will first hit them with 14.4VDC for a two hour time period and the battery will demand up to 20AMPS of charge during this time period. The Battery current demand will start dropping back as the battery start taking on charge. At the end of the two hour time period then the smart charger will drop back to 13.6VDC charge level and continue to seal the battery charge rate to its 90% charge status which takes another one hour time frame. If you leave the 13.6VDC Charge going on the same battery it will reach its 100% charge state in 10 hours or so additional time (total time 12-13 hours).

This is how may battery works at any rate...

based on my experience
Roy Ken

I would just start the van engine and charge the battery. At ~100 amps the battery would charge quickly. And no gas can and generator to worry about.

Trying to charge batteries from the unregulated circuit on the generator is a bad idea. It'll be very slow and unreliable. Best to get the battery charger of your choice and connect it to the generator for power.
Good luck / Skip

Yeah too bad you have to do that some of the topics really should be indexed.