[gregwatkins75]

Hi smart ones.

Currently building a camping style trailer,
Have a CTEK charging my second/aux battery that I run a fridge and two lights and a couple of sub point off...

Is there any reason I can't hook up a couple of correct gauge wires to the battery being charged by the CTEK
And run them via an Anderson plug to my trailer to also charge a smaller AGM battery?


Thanks in advance

[fordem]

Assumption #1 battery #2 is on the vehicle and battery #3 is on the trailer.
Assumption #2 battery #2 and battery #3 are both AGM.

Rule #1 - batteries should NEVER be paralleled unless they are of the same chemistry, capacity & age.

When you break rule #1, the end result is reduced battery life - I'm not going to go into all the permutations & combinations, but I will say that different chemistries require different charge voltages (bulk charge & float charge) and you'll end up overcharging one and undercharging the other - a very similar thing happens when the ages & capacities are different, but in these cases the impact is greater on the discharge side of the equation, and the batteries will quite rapidly "equalize" themselves, and I use the term "equalize" in a layman's sense (it does have a very specific meaning when discussing batteries & charging) - the batteries will soon behave as if they are as small as the smaller capacity and as old as the older battery.

In addition voltage drop across the cables & connectors (and yes, I did note that you stated "correct gauge wires") will cause the charge voltage at battery #3 to be lower than it is at battery #2, which will most likely result in undercharging - the CTEK will see battery #2, and adjust accordingly - in theory, you might "luck out" and because it's a smaller battery, it does charge reasonably well, but in reality how much charge it needs will be dictated by how much it has been discharged.

[gregwatkins75]

Thanks Fordem...

Both assumption 1 and 2 were correct.


So it sounds like my idea was bad...

Solar panel it will be.

[Marck]

You could manually switch between them. Split the circuits after the d250s. A 3 way battery isolator for 40 bucks will sort it out or for a few more bucks you could do it electronically but in the end a manual process. I'd do this and solar so you have charging choices. Or just get a cheeper DC to DC charger for your camper.

Marc