# NOT Just another Battery Query



## Ian_n_Suzy (Feb 15, 2009)

Hi,

This is not just another Battery Query, I suspect we need the info from an expert if at all possible please.

*Basically, I have been just been told by our Battery Retailer/Manufacturer that if wired in parallel and with the charger connected to the first battery, that the first battery will reach full and turn the charging system off.* (see below)

We have found over the past couple of weeks that our Batteries appear not to be lasting as long as expected (knowing approximately how much we have used).

The batteries had been left on charge on EHU at home for 5 days so I presume they are both full (if they are both working).

I left the Turbo Vent running on full (just under 3ah) and all the Lights on (2ah) which was drawing just under 5ah.

The batteries are matched 88ah, that were fitted new in May last year. I checked throughout the day the battery state (under load) and after 6 hours draw the reading was 12.1v, after 8 hours draw they were down to 10v, after 9 hours they were down to 9.8v and the next time I checked everything had shut down, after 11 hours.

I have just spoken to the retailer/manufacturer, of the batteries and this is what he told me: If the batteries are wired in parallel, then the charger must go to the positive of the first battery, and the earth of the second (or remove the earth, and earth to chassis). If they are not wired like this then when the first battery is full the charging system will stop charging the second battery.

He also told me if I have a Solar Panel this will work the same, it needs to connect to the positive of the first battery and the earth of the second to charge them both correctly. He also told me that the batteries don't need to be paired, as an example he commented that it doesn't matter if one battery is 1ah and the other is 99ah, it will still give you a 100ah 12v battery.

I'm sure that my charging system is set up on the first battery only (which is then linked in parallel to the second battery).

If all the above is absolutely correct, I need some modifications to my wiring, which I could honestly do without doing if at all possible.

What do you think?

THANKS IN ADVANCE


----------



## DABurleigh (May 9, 2005)

Well there's not an awful lot wrong with the above, but whether any of it matters one jot depends on the context and detail of which we know nothing.

So, what motorhome, what charger, how batteries connected by what, etc?

Dave


----------



## listerdiesel (Aug 3, 2012)

Sounds a little bit suspect.

If two batteries of equal size are connected in parallel, then the charger hasn't a hope in hell of charging either one in preference to the other.

How does the charger know? How can it apportion current to either battery?

It doesn't and it cannot.

I think you are being fed a load of cr*p.

Peter


----------



## Penquin (Oct 15, 2007)

Agree totally with Listerdiesel, both batteries will charge until it senses that that they are full - note THEY not it.......

I wonder if the battery manufacturer is saying things to cover themselves using a modicum of knowledge and a lot of flannel.......

Not an unknown way of dealing with customers - if you plaster them with knowledge they can rarely answer back as they are not the "experts" (thinking that an ex - spurt is a former drip under pressure) which is probably being used here......

Such a technique can be encountered quite often and reflects badly on the person spouting such junk - but it is difficult to argue with at the time unless one is of equal standing - difficult.

I would ignore what they say rather than listen carefully....

Dave


----------



## wakk44 (Jun 15, 2006)

I have heard this before re. 2 batteries wired in parallel,where it is desirable to wire the charging circuit to the +ve terminal of the 1st battery terminal and the -ve of the second battery.

My own purely unscientific findings do not support the theory.I can only comment on my own practical experience.In the last van I had 2 x125 A/H leisure batteries wired in parallel and 3 mts apart.(Unavoidable because of space considerations).

They were charged by 160 watts of solar and the conventional charger/alternator system.In 3 years of regular monitoring both batteries' terminal voltage were exactly the same.I must add that the connecting cables between the batteries was heavy duty to avoid any voltage drop.

edit;.....the charging circuit was wired to the 1st battery only.


----------



## rayc (Jun 3, 2008)

If the two batteries are connected in parallel with a descent set of linking cables then the two negatives are electrically the same place as are the two positive terminals. Therefore the statement "If the batteries are wired in parallel, then the charger must go to the positive of the first battery, and the earth[negative] of the second" appears nonsensical.


----------



## DABurleigh (May 9, 2005)

Well that's because you are all missing the significance of Ohm's Law when the batteries are remote from one another and not connected by thick cables.

Even when batteries are together it is recommended you connect to the positive of one and the negative of the other JUST so the cabling itself does not generate unequal charging and discharging currents.

That's why there is sound advice to match two 12V batteries in parallel, but why this matters not one jot when the two are well separated, so that the vehicle battery can be different to the leisure battery (and usually is, of course).

Dave


----------



## listerdiesel (Aug 3, 2012)

Capacities and Loads:

176ah at 5A load should give you 30+ hours
88ah at 5A load should give you 16+ hours

The wording of the original post re capacity is a little ambiguous, not sure if the capacity is 88ah or 2 X 88ah = 176ah.

Also, if the battery voltage was not checked before the start of discharge, you cannot assume that the batteries are fully charged.

Has the charger been checked?

Peter


----------



## listerdiesel (Aug 3, 2012)

DABurleigh said:


> Well that's because you are all missing the significance of Ohm's Law when the batteries are remote from one another and not connected by thick cables.
> 
> Even when batteries are together it is recommended you connect to the positive of one and the negative of the other JUST so the cabling itself does not generate unequal charging and discharging currents.
> 
> ...


Sorry, Dave, you're wrong.

Unless there is something radically wrong with the cables connecting the batteries in parallel, what we have all said is basically right.

Yes, there will be a slight difference due to volt drop at higher charge currents, but that will drop as the batteries come up on charge.

The practice of connection as you describe is not one that is particularly well-known on industrial battery systems, and you lose as much volt drop in the longer charging lead as you would have done in the linking wires, so a bit self-defeating. Your Ohms law statement applies to the charging leads as well!

The only question is whether the interlinking battery cables are heavy enough to take the charge current being applied by the charger.

Peter


----------



## Jimbost (Aug 25, 2012)

Postive of the first and negative of the second? I cant see that it will make much difference. If you have two batteries together in parallel you will have 12 2v (nominally) cells configured to produce a 12v supply. 
This does not really matter as provide the charger is running as it should through its charging cycle it will always end up with a floating/maintaince charge which should allow each cell to equalise in voltage. I worked with Electric Powered vehicles for many years and batteries, to get the correct voltage, can be wired in banks of series and/or parallel or even both in the same pack.
The thing to remember is that although individual cells are manufactured to be as identical as possible slight variances do happen, over time will mean that individual cells will discharge/charge at slightly different rates. A good charger will be programed to supply the correct charging rate to allow each individual cell to 'balance out' without overcharging. If the charger does not do this correctly or you have a dodgy or failed cell then the proper charging process will not have taken place. 
A failed or failing cell may, during charging, give the correct voltage and this can fool the charger into thinking that the charge cycle is complete. The charger will then go into maintaince mode keeping the cells topped up. When you start to discharge the cells the voltage in the faulty cell will initially act normally as current is drawn. As the faulty cell will have reduced capacity compared to the normal cells as the faultly cell reaches 'empty' the voltage will drop. This could be after hours or if the cell has failed after only a few minutes. This will mean that the overall battery voltage will drop effectively reducing the capacity of the battery. Even though the other cells are working normally your protection system if fitted will cut out or inform you or rapidly reducing capacity because it has detected voltages that indicated a nearly flat battery.

As you have two batteries to help diagnose which one may be faulty just connect and discharge one at a time. the faulty battery will discharge much quicker tha the other. If you have a normal lead acid battery configuration, have you checked each cell level? the faulty one will usually be well down in level compared to the others or it will show dark deposits on the cell walls. Unfortuantely you will not be able to do this with sealed or gel batteries.

It is possible you could have a faulty charger. Check the specs of yours (if possible)and see if the voltages you see on your meter matches the specs listed.


----------



## airstream (Jan 7, 2009)

*Only DAB*

Hi,
In all my considerable years - or am I just old? I have never seen correctly interconnect multiple batteries to form one larger bank.

When explaining the principle I revert to buckets of water saying that if you fill with a hose from on bucket to the next etc the first in line will fill first and the same when you empty

Electricity will always take the path of least resistance and all batteries have internal resistance as do the interconnecting wires

All interconnecting wires should ideally be of the same size and length

A better explanation is here

http://www.smartgauge.co.uk/batt_con.html

Ray


----------



## listerdiesel (Aug 3, 2012)

*Re: Only DAB*



airstream said:


> When explaining the principle I revert to buckets of water saying that if you fill with a hose from on bucket to the next etc the first in line will fill first and the same when you empty
> Ray


That analogy is for buckets connected in series, Ray, not connected in parallel, think about it.

Even in series, they do not act the same as a battery.

Peter


----------



## safariboy (May 1, 2005)

The problem is that the charger senses the voltage where it is. The resistance between the charger and the batteries will produce a voltage drop as will any resistance between the batteries. If you use very thick cables it should not matter but in practice we tend to use rather thinner ones than ideal.
The change in voltage with charge in a battery is very small. (Voltage is a poor way of determining the state of charge - though convenient and often used). The result could well be that the battery charger will switch to trickle before the second battery is charged. In the end both will be charged up but that may take some time.
There are charging systems with a separate sensor for the voltage and that might help you. Otherwise their advice seems sensible. Both batteries would then be connected to the charger by the same resistance.
You can get the same problem when charging from the alternator.


----------



## listerdiesel (Aug 3, 2012)

If you are at the end of charge anyway, then the difference due to wiring resistance will be negligible, let's put that to bed please.

As I said earlier, unless you have stupidly small cables between the batteries, there should be no measurable difference in what the batteries are doing or being charged at, at the point where the charger is deciding whether to drop down to float charge, and at that point we are talking about less than 1A charge current anyway.

A single-stage charger will just sit there doing its thing until the cows come home, which is what we have on our trailer.

Cable resistances ARE significant, but only at charging current where the volt drop starts to affect things, not at trickle charging rates.

Peter


----------



## listerdiesel (Aug 3, 2012)

Just to show what is done outside the motorhome industry:










These are dual 110V 200AH wet standby batteries installed at a sub-station in the Enfield area.

The batteries are fitted with fuses as you can see, plus blocking diodes at the common connection point where they come together to provide the supply for switch tripping on the 132kV and 33kV supplies.

The white items sticking up out of each cell in the 6V battery blocks are Aquagen gas recombination units, which reconvert hydrogen and oxygen that is given off by the battery back into water.

Paralleling batteries is quite common, but some rules apply when the strings get long and there are more than a couple.

In this case the batteries were fitted with dual independent chargers which could be switched to one of both batteries, really belt and braces stuff.

This was part of a refurbishment works that we carried out a couple of years ago.

Peter


----------



## rayrecrok (Nov 21, 2008)

Hi.

If all batteries are connected and a charge is applied they all charge at the same rate nearly equally until they are both eventually fully charged..

Or to turn it on it's head as far as the original post, instead of charging you are drawing current from the battery bank according to the OP one battery will go flat before the other then that next one would discharge, which is clearly bonkers as we all know they discharge equally as the stored voltage goes down..

I think I would be pointing at who ever said that, and laughing..

Unless I am totally wrong after all these years, then feel free to point and laugh at me. :roll: 

ray.


----------



## rayc (Jun 3, 2008)

A simple test the OP could do is remove the parallel links thereby removing 'battery 2' from the equation. Charge 'battery 1' and carry out the described discharge test. Is the result in line with the expectations for a 88ah battery? Swop the batteries over and repeat the test on 'battery 2'.
When he has that data replace the parallel links and charge as normal. When charging appears complete remove the parallel links again and carry out the discharge test again on each battery in turn. Compare to the data in the first set of tests.


----------



## Fatalhud (Mar 3, 2006)

Hi Ian n suzy

As far as i am aware the dealer is correct,
You get a better charge and also a more efficient discharge connecting across the 2 batteries

Link 1

http://batterytender.com/resources/connecting-batteries-chargers.htm#answer3

Read notes relavent to diagram 9

Link 2

http://www.smartgauge.co.uk/batt_con.html

the example uses 100Amp discharge, but the effect is still relavent for lower loads

I was shot down in flames on another post regarding this subject so I have put my hardhat on ready :wink: :wink:

I will be interested to see other posters who say it makes no difference provide documented proof :wink: :wink:

Alan H


----------



## rayc (Jun 3, 2008)

Fatalhud said:


> Hi Ian n suzy
> 
> As far as i am aware the dealer is correct,
> You get a better charge and also a more efficient discharge connecting across the 2 batteries
> ...


So are you saying that if I move one of the the charger leads 300mm down a 35mm csa link cable it is going to make a discernible difference?

My 2 x 110ah batteries perform as I would expect them to when charged with the on board charger, solar panel or alternator.
I have carried out the tests I recommended in my previous post and can measure no discernible difference to each batteries performance when charged individually or as a parallel bank.

The document you link to says on the matter: 
"In Figure 9 we see a pair of 12-volt batteries connected in parallel. This 12-volt battery pack is connected to a single 12-volt charger. Note the blue wire designated W1. The purpose of this wire is to balance the voltage drop evenly across both batteries and each wire during charging. This is not critical for lower current chargers, but when you start to get into the 10 amp and above range, the voltage differential can be significant.


----------



## airstream (Jan 7, 2009)

*Read the Smartgauge link*

Hi,
If folk read the link - mine or other SmartGauge you will see beyond any doubt that the connection method for lead acid batteries is as the diagrams

Below an an example of paralen "daisy" chaining taken from the Smartgauge link

"Battery internal resistance = 0.02 Ohms
Interconnecting lead resistance = 0.0015 Ohms per link
Total load on batteries = 100 amps

The bottom battery provides 35.9 amps of this.
The next battery up provides 26.2 amps.
The next battery up provides 20.4 amps.
The top battery provides 17.8 amps.

So the bottom battery provides over twice the current of the top battery.

Clear enough?

Peter, you missed the point water will flow through the easy route first so 2" pipe to first bucket at same pressure will always fill before next and others that "T" off the same supply

Through in the fact that most second/third batteries are wired in smaller cables and have fuses the chance of equal charge discharge when the load/charge is applied to the terminals of one battery is nil

So with my water example 2" pipe to first then 1/2" to the others

Not scientific but a simple way of explaining a very complex issue 
and only trying to help

Ray


----------



## Murano (Mar 22, 2006)

Alan H
No need for a hardhat as far as I'm concerned. What you and the dealer say is the correct method. I cannot prove why but after many years of working with large batteries, that is the method that was used, and that I still use on the my van.

Dave


----------



## listerdiesel (Aug 3, 2012)

Fatalhud said:


> http://batterytender.com/resources/connecting-batteries-chargers.htm#answer3
> Read notes relavent to diagram 9
> Alan H


Read what I said, and then this bit which is below Diagram 9:

"In Figure 9 we see a pair of 12-volt batteries connected in parallel. This 12-volt battery pack is connected to a single 12-volt charger. Note the blue wire designated W1. The purpose of this wire is to balance the voltage drop evenly across both batteries and each wire during charging. * This is not critical for lower current chargers, but when you start to get into the 10 amp and above range, the voltage differential can be significant.* The blue wire W1 must be connected to the opposite end of the battery pack as the black wire at the top of the battery pack."

What they don't say, is that the voltage drop in the blue coloured cable will be higher due to the additional length of cable required on a MH, and thus negates any beneficial effect that it 'may' have.

Once the batteries come up on charge, it all evens out anyway, as I said earlier. Voltage losses at low current are not significant as they say in their text, they also say that "when you start to get into the 10 amp and above range, the voltage differential can be significant" which nobody is disputing, but we also assume that the charger is left on to complete the charge.

Showing theoretical diagrams is fine, but real-life operations make it a different scenario.

Peter


----------



## GEMMY (Jun 19, 2006)

So when you have 3 batteries in parallel, where do you conect the wires of an inverter, one lead on the first battery, 2nd lead on the last battery :wink: 

tony


----------



## Fatalhud (Mar 3, 2006)

GEMMY said:


> So when you have 3 batteries in parallel, where do you conect the wires of an inverter, one lead on the first battery, 2nd lead on the last battery :wink:
> 
> tony


Yes 
look at the examples on the second link (method 2)


----------



## grizzlyj (Oct 14, 2008)

As someone with no expertise, can I ask;

Why isn't a charger going from +ve on batt 1 to -ve on batt 2 (in parallel as far as the camper is concerned) going to experience 24v? Maybe similar to Gemmys question above.

And what happens if the buckets have custard in them?

Interesting stuff though, thank you


----------



## listerdiesel (Aug 3, 2012)

To try and finish this one off, while there are lots of schemes for connection of batteries and chargers, the wiring as detailed in the original post would not cause any significant difference in charge to either battery, but we do not know what the state of charge was at the time of the discharge test that he carried out.

Peter


----------



## Ian_n_Suzy (Feb 15, 2009)

Hi,

THANKS for the numerous replies. 

I am going to try each battery individually and see what results that returns. 

(there are 2 x 88ah batteries and the connecting leads are thick/high quality ones (can't remember spec), as is the Solar Cable to avoid voltage drop.)


----------



## alberts (Nov 14, 2012)

Your batteries are perfect.

cold temperature loss of capacity, charger that doesnt fully charge to 14.7v and discharging at a high rate of 5 ah. why on earth would anyone expect more than 40ah useful power from a mere 170ah ?


----------



## lgbzone (Oct 8, 2008)

Ian_n_Suzy said:


> Hi,
> 
> This is not just another Battery Query, I suspect we need the info from an expert if at all possible please.
> 
> ...


Hi Ian

essentially there are two points the guy is making;

1. if wired in parallel, then the charger must go to the positive of the first battery, and the earth of the second.

2. if wired in parallel they don't need to be matched, mixing 1ah and 99ah is perfectly fine.

in both scenarios i think he's taking something that's sound, to such an extreme, that it looses value when applied to leisure batteries in a motrhome. Batteries are stressed when either being charged or discharged, it's almost insignificant at low currents but far more significant at higher currents, the trick is to try to ensure that all batteries are stressed relatively equally.

1. ideally they would be connected as he states, both for charging and discharging, there are loads of experiments, both on and off the internet, that show how batteries in a bank are stressed far more equally (under high load) when wired in the ideal manner. in reality i reckon the charge and discharge rates are normally so (relatively) low in a motorhome, that it would make very little difference, if at all, and certainly nothing you'd notice. he makes it sound as if the second battery will only ever get half charged or something, which isn't the case at all.

2. again he's gone too far; they don't need to be exactly the same capacity but they should be somewhere near, if you paired 1ah with 99ah the 1ah battery would be duff very quickly, especially if the discharge rates are relatively high. batteries have a "C" rating for both charge and discharge where C represents the capacity of the battery, and going beyond the C rating potentially damages the battery. so for example; if the batteries above both have a charge rating of 1C and a discharge rating of 2C; charging at above 1amp or discharging above 2amp could start to damage the 1ah battery, whilst the 99ah battery could be charged at up to 99amp and discharged at up to 198amp. (the C ratings i've used are just examples)

Personally i don't think it's worth your effort rewiring the connections to the batteries unless it's easy to do so, in which case i would, but i often like things to be ideal.

HTH

Lee


----------



## Ian_n_Suzy (Feb 15, 2009)

Just a quick update.

As I suspected the Batteries were unserviceable and well down on power output. After a full individual charge, I put a load of 2.2amps through them individually and managed 8 hours from one battery and 8 hours 50 mins from the other (less than half capacity).

I also had them tested on a Bosch Battery Tester and this also showed them as being unserviceable. 

The supplier is changing them under warranty but I have decided to put some money towards and buy slightly better 125ah Deep Cycle versions.

THANKS for the replies.


----------



## oldun (Nov 10, 2005)

listerdiesel said:


> Sounds a little bit suspect.
> 
> If two batteries of equal size are connected in parallel, then the charger hasn't a hope in hell of charging either one in preference to the other.
> 
> ...


Fully agree with this but will the charger cope with the two batteries?


----------

