Question about adding 2nd battery and switch

[Herk7769]

Originally Posted by Triguy

I can't explain why your dad's batteries would charge that fast. I would guess that the 15 minutes your dad uses to charge his batteries is applying a surface charge only. I know it takes hours for my batteries to charge from 50%. Even when I had a group 27 on an old camper, it would take hours for the absorption charge and hours longer after it hits about 90% charged.

That is easy. It takes about 15 minutes of charge to bring a battery that is under 12 volts to read more than 12 volts. That is NOT "charged."

There is no "capacity" replacement when you do that and it destroys batteries as it counts as a charge/discharge "cycle" of which there is a limited amount in a new battery.

"It works" is not the same as "its smart."

In fact in this graph you can see the sharp upward spike when you first put the charger on the battery. In order to replace AH capacity the charger must stay on for hours.

[jar3316]

That's good to know I have only had this trailer since Nov '11 and hadn't thought much about the Electrical system on it yet. with the exception that it had NO 12VDC jacks anywhere on it. Now it has them everywhere.

My old Tent trailer didn't have a charger on its converter so we added one, glad to see that has changed.

Batteries seem to be one of those hot button topics like oil to a motorcycle forum.

[Triguy]

Originally Posted by herk7769

In fact in this graph you can see the sharp upward spike when you first put the charger on the battery. In order to replace AH capacity the charger must stay on for hours.

Thanks again to the Herkbrary!

[MikeInColo]

Just trying to get my head around why your switch enables you to use the first *or* second battery? I understand off/on but why would you want to only use one or the other battery singularly when using with an RV?

[Herk7769]

Originally Posted by MikeInColo

Just trying to get my head around why your switch enables you to use the first *or* second battery? I understand off/on but why would you want to only use one or the other battery singularly when using with an RV?

This will be required if you have two batteries that were not bought and placed in service at exactly the same time.

This way you can charge each battery individually and when in use get all that each is able to give.

When pairing batteries that are different in age, internal resistance, cycle life (place in service date and number of actual charge discharge cycles)) , or manufacture, one battery will be the "stronger" battery and one will be the "weaker" battery. The batteries will not charge properly; one will work much harder than the other; and both will operate at reduced capacity. Eventually both will fail much earlier than if they were used individually.

Battery pairs must be changed out at the same time. When you want two batteries in your camper, they need to be as identical as possible.

IF you can't do that for some reason, using a selector switch to use them one after the other is your only choice to get maximum life from your house batteries.

Practical considerations : BATTERIES AND POWER SYSTEMS

Deep Cycle Battery FAQ