Running two different AH batteries together?

[mudski]

I'm going to start the wiring of adding a second battery to my camper soon. Do I need to get the second battery that of the same AH rating of the battery that I already have? What will happen say if I get a 130AH battery and my first battery is 105AH?

Cheers.

[Drew]

My understanding is that they should be as close as possible ie same battery model etc Having different capacities causes problems.

[mudski]

My understanding is that they should be as close as possible ie same battery model etc Having different capacities causes problems.

Thats what i am thinking. The lower AH battery will only limit the higher AH batteries capacity/ ability...

[AB]

I think I asked this same question a while back and ET mentioned they should be the same otherwise they won't charge properly. Larger ah wont get full charge?

Assuming you'll be running them both from a single management system.

Hopefully someone can explain in more depth.


Sent from my iPhone using Motorculture mobile app

[Cuppa]

What will happen say if I get a 130AH battery and my first battery is 105AH?

Cheers.

No problem with different capacities of the same type of battery.

"There is no problem parallel charging similar type batteries of the same voltage but of widely different capacities. They look after themselves. 'Each draws a proportionate share of the available charge, and all reach about the same level of charge at roughly the same time,'(Ample Power Company 1990). They discharge in much the same way.”

Taken from http://www.caravanandmotorhomebooks....batteries.html

Note the word similar - this refers to batteries with similar charging requirements.

I have a set up with two N70 size (D31 - 75Ah) Yellow Top Optimas paralleled to two 90Ah Fullrivers without problem. The Optimas replaced ‘wet’ starter batteries which I got 5 years out of. The Optimas are now over two years old & the Fullrivers are over 8 years old, system is still working well.

[paulyg]

Wont they be different anyway when one is a starting battery and the other is a deep cycle battery?

[Drew]

A little more info http://www.homepower.com/articles/so...eries-parallel

[Cuppa]

Wont they be different anyway when one is a starting battery and the other is a deep cycle battery?

As mentioned I had 2 wet starters (24v) paralleled with two Fullriver AGMs (deep cycles), the Fullrivers are still going strong & the wet starters lasted for over 5 years (They would probably have lasted longer if I hadn’t neglected to top them up & inadvertanly ran them dry). 5 years for starter batteries is pretty good so clearly the paralleling/charging arrangement did them no harm. You can read widely differing opinions on the net varying between ‘it’s ok’ to ‘under no circumstances do it’. My direct experience suggests ‘it’s ok’. The one issue I had with this set up, is that the wet batteries had a faster self discharge rate than the AGM’s, & if left for a few days without being charged would pull the AGMs down to the VSR cut off voltage. In practice this was not an issue as when the vehicle was in use the ‘extra’ capacity provided by the starters was used each night, & when the vehicle was not in use they were connected to a CTEK charger in ‘supply mode’ preventing any drain.

[mudski]

Thanks cuppa. I was kinda hoping you'd pop your head in...As you da' man.

[alfonso]

just a quick note . I was told when joining batteries to have positive on one battery and negative on the other for charging as this creates the vision of one large battery