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mudski
5th March 2014, 07:21 PM
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
5th March 2014, 07:51 PM
My understanding is that they should be as close as possible ie same battery model etc Having different capacities causes problems.

mudski
5th March 2014, 07:57 PM
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
5th March 2014, 08:03 PM
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
5th March 2014, 08:06 PM
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.com/articles/interconnecting-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
5th March 2014, 08:07 PM
Wont they be different anyway when one is a starting battery and the other is a deep cycle battery?

Drew
5th March 2014, 08:15 PM
A little more info http://www.homepower.com/articles/solar-electricity/design-installation/ask-experts-batteries-series-parallel

Cuppa
5th March 2014, 08:31 PM
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
5th March 2014, 08:34 PM
Thanks cuppa. I was kinda hoping you'd pop your head in...As you da' man.

alfonso
21st August 2014, 05:15 PM
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

Cuppa
21st August 2014, 08:46 PM
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


I expect you are referring to connecting two batteries together in parallel (i.e. keeping the same voltage of a single battery whilst increasing capacity). If so your informant was correct & it looks like this. You can connect loads to just one of the batteries, they will still charge & discharge as one, but the pictured method is considered better (although I’m not exactly sure why).
http://www.nissanpatrol.com.au/forums/attachment.php?attachmentid=48558&stc=1


If connecting more than two batteries together in parallel there are several ways to do this, the article here (http://www.smartgauge.co.uk/batt_con.html) suggests which are the better options.
In my Patrol the three aux batteries are connected in the star pattern (Method 3 in the above link) similar to this:

http://www.nissanpatrol.com.au/forums/attachment.php?attachmentid=48559&stc=1

mudski
21st August 2014, 08:48 PM
I think cuppa, he means +ive on one battery to the -ive on the other battery. Which would turn it into a 24V battery.

Cuppa
21st August 2014, 09:44 PM
I think cuppa, he means +ive on one battery to the -ive on the other battery. Which would turn it into a 24V battery.

Yeah I thought alfonso’s post could have meant either, which is why I made my post to clarify. Not many Patrols had 24v systems, but a few did. When connected as you suggest (in series) the voltage increases but the capacity remains the same as that of a single battery. It would not be a good thing to connect a second battery like this in a 12v vehicle!