charging a pair of batteries in parallel

Batteries in separate compartments are such a rotten solution. Like Scott just said above, these discussions usually turn more complicated. In the long run, all batteries have a certain number of charge/discharge cycles before they are done. The problem with 2 12 volts in series (and the good thing about 2 6 volts are in parallel) is with 12s, since no 2 batteries are exactly the same, the better 12 volt will always be attempting to charge the weaker one and when the charger is on, it will always be charging the weaker one while overcharging the stronger one. If you look around, most people get less than 5 years out of 2 12s but most 6 volts last about 7 years. The 6 volts in series don't have the self-discharge situation of 2 12s in parallel. Not a reason to just swap out batteries but when it comes time to replace the 12s, you will get more value out of switching to 6s. The separate compartment situation does make that a challenge, though.

OP, one thing to know about this forum is we can take the most simple subject (like this one) and add complexity and technical garbage to the point or being ridiculous.
The bottom line since your battery's are in parallel, simply connecting the charger to one of them will charge both. Period! Just like the millions of trucks on the road that are wired that way from the factory and live full happy lives.
We can add technicalities on getting them charged a half a percent better (or what ever, it's minuscule) by jumping through all sorts of hoops but the bottom line remains - your good to go.

Depends on how they are wired. If balanced--no problem, if not it can be done but won't give you the best possible results.

http://www.smartgauge.co.uk/batt_con.html

Not what you asked, but I'd check into how the dealer connected the parallel wiring. Did they run the converter negative and positive leads so that the two batteries charge equally on shore power? Or take the easy way out and run two leads from one original battery to a new location for an additional battery.

Second scenario will result in unequal battery discharge and charge every day.

Gonzo42 wrote:
Yes, it can be done, but being as batteries are always somewhat different, any naturally occurring difference in voltage could mean that they will both charge to the lower voltage value of the two. Probably won't be a problem for you as long as you don't do this always.

And when you are done camping, charge them individually so they get the maximum charge.

Yes, it can be done, but being as batteries are always somewhat different, any naturally occurring difference in voltage could mean that they will both charge to the lower voltage value of the two. Probably won't be a problem for you as long as you don't do this always.

In any case as long as they are both in good condition, they should supply current to all your devices.

2oldman wrote:
yep

Yep X2!

yep