Can you charge car battery thru the camper..?

Hi Craig,

I've got a Sindwinder dual battery system. Its about 2 years old. That's where I reckon the idea might let me down (only 1 way flow thru the isolator) but considering the wiring to the Anderson plug/trailer battery is straight off the 2nd battery I reckon I should atleast get charge to the 2nd battery????

I'm not really worried about the starter battery anyway its just that I don't use my vehicle often so I know that the DC battery does get run down (loses voltage) over time and I always have the camper hooked up to the vehicle atleast 24hrs before heading off (to get 3way fridge cold) and this would then mean that it gets a good charge before we head away....without having to pull out my other charger and connect it directly to the the battery.

Yes in that case the 240v charger will top up your 2nd battery in the car as well if the cable size between the two is appropriate. Probably just need to check the specifications of the charger to ensure it's suitable for the combined amp hour rating of the car & camper. (Usually have a range for example of between 80 & 300 ah)
Cheers Craig..............

Thanks Craig. Yeah I have 6 B&S cable to the camper and the charger is rated to 300ah so it should do the trick.

Wouldn't the 2 batteries level themselves out if he connects the trailer battery straight to is Aux Peter?

That's what I thought.

Two batteries do not equalise when you connect them together. There was a long thread on this some time ago.

When you have one charged and one discharged battery, if you charge them together the charger will quickly raise the system voltage to a level higher than the float voltage. This high voltage will be maintained until the charge level of the flatter battery rises to a level where the charging current reduces to a level where the charger drops back to the float voltage level. When a battery is fully charged it should not be subjected to a charge voltage higher than its recommended float voltage. This is referred to as overcharging. During the period between the commencement of charging the auxiliary battery and the charger dropping back to float the campers house battery will be subject to an overcharge voltage.

You will note I said "if the camper battery is full or nearly fully charged." May be I should have also added that if both batteries are discharge or partially discharged AND they are of the same chemical construction then it is permissible to charge them in parallel. For charging in parallel they need not be the same size (A/H) - the larger or flatter battery will accept more current and they wil reach full charge together.

PeterD

Thanks Peter. That's why I love this forum....you learn something new everyday. So basically it would probably be a good idea when I get home and need to top up both batteries but not before I leave when the one in the camper is already fully charged because its been on the charger constantly. Looks like I will have to do the vehicle battery manually then.

Thank you Peter, I didn't realize that. Good to find a competent answer, hey?
You are never too old to learn I suppose :)
Cheers, Udo

So that means that if the camper trailer battery is discharged and you charge off of the vehicle when you are driving you could cause over charging to the vehicle battery and have it explode.

When you first start the vehicle, depending on the battery isolator, but with most popular systems the Cranking battery will be fully charged first, according to Redarc it takes just a few minutes then the Aux battery is connected and is also charged.

There are hundreds of possible variables to this scenario.
The Aux battery is never fully discharged anyway is it, because it has a battery cut-out switch in the fridge or in-line ??

When the Cranking battery and the Aux battery are connected in parallel by the battery isolator, the two batteries are 'seen' as only one large battery by the Alternator regulator, with only one voltage number not the two separate voltage values as they were previously.

Mainey . . .