# Twin Batteries linked in parallel of different capacities?



## Curtisden (Mar 23, 2009)

Is it either wise or foolish to link to different capacity batteries together in parallel for leisure use? My Autocruise has room from two 95Amp batteries under the floor in the battery box but came with only one. claimed in the sales information as 95Amp. I can not find this size on sale but have a old deep cycle 85Amp. Can I link this together?
I am told both good and bad. That one will drain quicker and ruin quickly oxidising as the other drains? That the Two should be the same size and age? 
It has crossed my mind to only link the - and put in a changeover switch between the 2 + but then only one can be charged together? Still means flat batteries and problems.
Any advice? http://www.motorhomefacts.com/images/icon/icon5.gif

Peter


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## clive1821 (Mar 27, 2010)

I think if I was you, I would just replace both and have new ones and then you have a good point to start with of the same ampre hour.... use something like power max batteries for example....


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## andyandsue (Sep 7, 2008)

*battery fun*

first thing is check condition of ex bat , fluid level is first if not sealed, then fully charge it leave it to stand 2 days with nothing connected and have it checked under load at a good battery shop...this takes 10 secs and should cost nowt. then decide its capacity and double up same size and type... this is only worthwhile if the exsisting bat is brand new. if exsisiting bat is old then scrap it( you will get about £6 at a scrap yard) and buy 2 new ones of same size and capacity.....no need to bother with gimiky hyper expensive just buy simple good quality bats. if u are buying and fitting a new set of bats now is the time to clean up/replace connectors and cables whilst your at it ....best of luck and wear splash glasses and thin gloves whilst working( we do and we get paid for it so its not ELFAND SAFETY gone mad


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## moblee (Dec 31, 2006)

I asked the same Question awhile ago it may help you peter.

http://www.motorhomefacts.com/ftopic-104195-0-days0-orderasc-.html


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## Antonia (Apr 27, 2008)

*Two Batteries*

If I wanted to do this cheaply I would common ground them, then I would fit a quick release to the + terminal of one. So, when one runs down you can just unclip and connect to the other.

As for charging seperately, well if you wanted to charge both at the same time you could use a couple of Diodes. Or swap that as well.

Simples.

There are of course 'better' and more expensive ways of doing it, as always.

Regards

Antonia


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## peejay (May 10, 2005)

This might be of interest - Autosleepers don't seem to think there is a problem fitting batteries with a differing output is a problem....

http://www.motorhomefacts.com/ftopicp-206757.html#206757

Pete


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## CliveMott (Mar 10, 2008)

Providing both batteries are the same technology (both wet or both gel) then most compromises will provide an advantage. Ideally you have a matched pair of batteries but on the other hand you don,t scrap durable batteries either.

Charge them both first so you don,t get any suprises when you initially link them.

C.


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## eddievanbitz (May 1, 2005)

CliveMott said:


> Providing both batteries are the same technology (both wet or both gel) then most compromises will provide an advantage. Ideally you have a matched pair of batteries but on the other hand you don,t scrap durable batteries either.
> 
> Charge them both first so you don,t get any suprises when you initially link them.
> 
> C.


Brilliant answer! 100% agree

Eddie


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## CliveMott (Mar 10, 2008)

Cheers!
C.


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## H1-GBV (Feb 28, 2006)

I joined an old (4y?) 80Ah battery to a new 115Ah battery. The advice was not to do it, and probably I've downgraded the entire system to 150Ah (or thereabouts) BUT it's only cost me the price of one new battery.

So far they have worked fine for 3 years together.

WHEN they die, I'll consider matching items.

IF you have lots of money, you might want to spend it - Gordon


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## Curtisden (Mar 23, 2009)

Hi
Many thanks for the posts.
Spoke to a battery company engineer yesterday when I had or tried to have the battery tested.
1. Seems that a 95 amp hour is probably just a good quality 85 amp just with more lead inside but he does not sell them or have a demand. So stuffed.
2. He sees not real problem in linking and believes that if there is a problem down the line it will be the older 85 amp that will fail first.
3. Asked if my dealer sold said size. NO! So what would he fit? Either take out the 95 and fit 2 85 amp at my cost!?! or fit a new 85 amp anyway?!?
So why do Swift fit these odd sizes?
Made up my mind to carry the second battery only when I am away for any length and either fit a swap over switch or just extend the clips wires to reach both batteries in the underfloor box. That way I can take a fully topped up in the garage second unit and keep the 95 amp topped up in the van.
Oh yes did you know that you can't have a Deep Cycle battery load tested as a car type. Only voltage test for some reason. 
Thanks to all


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## Curtisden (Mar 23, 2009)

*Twin Batteries Answer from Swift.*

Seems that the EU **** has re calibrated the way batteries are described and that a 95Amp hour is an old 110Amp in all but name?
That came from Swift Technical help line.
I only have one more question WHY?
Thanks to everyone.
Peter
PS So I can link a old 110 to the new 95, but not to the old 85. Luckily I have both from my old Abbey.


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