# Tech advice re compatability of leisure batteries



## taildj (Jun 4, 2006)

I had to suddenly purchase a leisure battery in France when mine died a couple of weeks ago. I now want to add an additional one to increase capacity. The French battery is 92amp hrs but in the UK I can only find either 85 or 110 amp hrs

Can anyone tell me what are the implications of putting a 110 alongside the 95 amp hr battery, or is it a no go

David


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## Scotjimland (May 23, 2005)

Hi David 

If the batteries are of different ah. the voltages across the terminals of each battery will drop differently, this will lead to a current circulating from one battery though the other, depleting the remaining charge. 

So, a lot will depend on how you intent to use your van, if you mainly use hook ups it will make little difference but if you intend to free camp or mainly off hook up my advice would be to fit two new matched 110ah.


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## wakk44 (Jun 15, 2006)

Make sure you have the correct setting on the mains charger for the type of leisure batteries you fit-some Hymers have a gel or lead acid setting.

Steve


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## JockandRita (Jun 1, 2005)

wakk44 said:


> Make sure you have the correct setting on the mains charger for the type of leisure batteries you fit-some Hymers have a gel or lead acid setting.
> 
> Steve


I can concurr with Steve's comment.
Upon getting the Hymer home, we discovered that the batteries were bone dry. Topped up and recharged (shot really) they were checked a fornight later...........bone dry again.

The switch on the base of the "Elektroblok" was in the gel setting, and the batteries were lead acid.
3 x new batteries, switch in correct position, and 2 x years down the line, and all is well. Not even needed topping up. 8O

Jock.


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## DABurleigh (May 9, 2005)

That's curious, Jock. The gel setting is "easier" on batteries, mainly a reduced maximum terminal voltage. If you have any more technical gumpf on the charger battery settings I'd be interested.

Dave


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## JockandRita (Jun 1, 2005)

DABurleigh said:


> That's curious, Jock. The gel setting is "easier" on batteries, mainly a reduced maximum terminal voltage. If you have any more technical gumpf on the charger battery settings I'd be interested.
> 
> Dave


Hi Dave,

I happen to know that you are a *very *clever person, and, very technically minded, so please forgive me if I detect an element of sarcasim in your above statement.

I was not giving technical gumpf to to Taildj, (David), I was telling it as it was when we took over ownership of our MH, and concurring with what Wakk44 had posted re the change over switch.

Had the previous owners looked after the batteries the way that they should have done, then we would still be £240 in pocket.

The original factory fitted battery (1), was gel, hence the position of the switch. I identified a problem with the lead acid replacement batteries (3) cooking themselves dry, and investigated. I even isolated the solar panel connection through my process of illimination. when the problem still existed, I then took to reading up on the "Elektroblok".
You on the other hand, would probably have gone straight to the problem with the technical knowledge that you have.

Having found the change over switch, I then replenished the "almost dry" batteries for a second time, observed the fluid levels of all the cells over a period af weeks. When I was happy that they were no longer "cooking themselves, I reconnected the solar regulator, and observed further.

Only when I was convinced that the problem had been sorted, did we then replace the "shot" batteries with 3 x new Elecsols 100's at the cost of....................£240. 8O 
That was 2.5 years ago, and no problem. That flags up with me, that perhaps I have done something right. :lol:

If you care to trawl through my previous posts, (I can't be bothered), you will see that Boff gave me some good advice on the matter, for wich I was grateful. There wasn't an element of sarcasim in his reply, and he too is quite a clever person.

Sorry if my offerings above, are not in the "technical gumpf" category that you were hoping for.

Jock.

P.S. Off topic I know.....an excellent write up on France. I just wish that my night time photo of Le Mont St Michele, was as clear as yours, using my shirt pocket camera.


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## DABurleigh (May 9, 2005)

Thanks, Jock. That's the second time in a few hours that I've been told my posts are sarcastic, when none was intended. Even re-reading it, I don't see where; it seems a straightforward neutral question to me. 

My motivation for the question was that, as I try to give accurate advice, your battery experience was at odds with what I have suggested a number of times to those who want the maintenance-free benefits of gel without the price premium, namely to buy cheap lead-acids and set the charger to gel. If that advice is wrong I'd simply like to understand why.

Anyhow, in terms of me "going straight to the problem", no, I don't understand at all what was happening. I'll look up Boff's post in due course.

Dave


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## taildj (Jun 4, 2006)

Thanks everyone. Yes I knew about the switch on the electro block. I am trying to source a 95amp hr battery so that should solve the other problem. As usual members are knowledgable and helpful . Thanks again


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## olley (May 1, 2005)

Hi the theory is that they should be matched in capacity, age and if possible make, however I have never seen any practical tests to back this up, while I have spoken to a few practical people who ignore this and fit whatever they can get their hands on without any apparent problems. 

So I wouldn't be to bothered about mixing one slightly bigger/smaller of the same type. Just my opinion.

Olley


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## Snelly (Aug 20, 2005)

Not that my advice is worth much now... but I concur, batteries are better matched. If you have a big battery and a little battery, the little battery will constantly pull power from the big one.

Go for Numax... the CVX series, beautiful battery.


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## olley (May 1, 2005)

Snelly said:


> If you have a big battery and a little battery, the little battery will constantly pull power from the big one.
> 
> Go for Numax... the CVX series, beautiful battery.


Why? if they both discharge at the same rate if separate, why should it make a difference connecting them together. 
Irrespective of battery capacity the terminal voltages will be the same (assuming they are in good nick) so unless there is a difference in potential, current cannot flow.

Not saying your wrong, just want to know why? :lol:

Olley


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## Snelly (Aug 20, 2005)

Olley, without googling, I have to admit I was quoting from my memory of something i'd once read, so I could be wrong. No time to research, trying to get stuff ready for going away! Maybe someone with a bit of time can look it up???


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## wakk44 (Jun 15, 2006)

Whenever you put 2 or more batteries in parallel,they must be of the same capacity,or the smaller one will be overcharged while the larger one will be undercharged,it's because of the different internal plate resistance of the leisure batteries.

They should also be of a similar age and condition because if one is older and had more use then the sulphation on the plates of the older battery could pull the newer battery down.This is why the experts advise always use the same make,age and capacity of leisure batteries when changing them.

Lead acid batteries are relatively cheap and in my experience it has made sense to simply replace them both together rather than mess around trying to get a bit longer out of old batteries.

Steve


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## olley (May 1, 2005)

Hi Steve heard that before but to me its doesn't seem logical. My thinking is this:

Two batteries 1x100amp 1x200amp both terminal voltages the same, connect them in parallel, because their terminal voltages are the same no current flows.
I start charging, charging current is dependant upon voltage, as they are connected the terminal voltage must will stay the same, as the smaller one charges quicker its internal resistance will increase so it will accept less charge, so how can one be overcharged? 

On discharge the smaller one will discharge quicker its voltage will drop so the larger one will take on more of the load, but its twice the size so that's what I would expect.

In practice the voltages will stay the same, only the current flowing in the wires will alter. 

I am thinking off it like two water tanks 1x1000 gallons 1x10 gallons both the same height so that the water levels are the same, connect them together at the base and draw water off, the levels diminish at the same rate, and similarly when I fill them.

Olley


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## JockandRita (Jun 1, 2005)

Hi DAB,

You have a PM.

Jock.


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## peedee (May 10, 2005)

wakk44 said:


> Whenever you put 2 or more batteries in parallel,they must be of the same capacity,or the smaller one will be overcharged while the larger one will be undercharged,it's because of the different internal plate resistance of the leisure batteries.
> 
> They should also be of a similar age and condition because if one is older and had more use then the sulphation on the plates of the older battery could pull the newer battery down.This is why the experts advise always use the same make,age and capacity of leisure batteries when changing them.
> 
> ...


I have wrestled with this question many a time and do not support the view of you cannot do it or that "the smaller one will be overcharged while the larger one will be undercharged," However, I do support the rest of Steve's statement. I think the reason it is recommended to "always use the same make,age and capacity of leisure batteries when changing them." is more to do with practicality than technical reasons in that they should both die equally gracefully rather than one dieing and dragging the other down. I have certainly run different makes and ages of battery in parallel but you must monitor the individual cell performance carefully if trouble is to be avoided. The same is probably true of different capacities but it is over 40 years since I had to consider such things and my aging brain hurts thinking about the technicalities but really it only boils down to two similar 12 volt e.m.f.s with dissimilar internal resistances in parallel which will look, to an external source/load, like a single 12volt battery of lower internal resistance than either of the two batteries used individually.

peedee


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## taildj (Jun 4, 2006)

...and I thought that my original question would be answered relatively simply. Thanks everyone for their comments . They are much appreciated.


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