# Testing leisure batteries



## Kev1 (Apr 4, 2011)

We have a Hobby 750
Fitted with 3 x 100a leisure batteries of varying ages.
It has an 80w solar panel
and a generator.
Whilst away for 3 weeks wild camping .
Driving at least 4 hours per day
The battery monitor kept showing low batteries 
sometimes down to 11.7v

And two nights we lost cabin lights entirely.
We ran the generator as well to charge up the batteries.
The only items drawing on the batteries are internal lights and water pump

We have now come home and plugged into the mains
overnight the batteries now read 13.2v on the voltage monitor

I just took them dow to our local garage and he put a discharge rod on each battery for about 3 seconds 
They read 9 and did not drop. He says they are ok

So the questions are:
1) Has he tested them properly

2)Whats the best way of testing each battery to see if it's either o.k. or needs renewing.

Any other suggestions much appreciated

Kev

I


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## clive1821 (Mar 27, 2010)

Hi there's various ways of testing batteries, both technical and the rule of thumb.... one way is to make sure the batteries are fully charged ie when fully charged and with the charger on you would expect to see around 13.8volts accross the batteries. Then disconect the batteries and conect a load accross each of the batteries, for example a inverter with say a 150watt lamp conected, which would consume around 18amps so if you have a 110AH battery and taking into account the losses of the battery I would expect the load to keep working for around 4 hours if that works for that time I would say that battery is ok.... most inverters will stop working if the battery volts drop below 11.5volts and thus saving the battery getting totaly discharged.... its a usefull test and gives you a practical test. I hope that helps....


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## Kev1 (Apr 4, 2011)

Hi Clive given i have 3 batteries do i do the test individually
i.e 
one battery at a time

cheers

kev


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## clive1821 (Mar 27, 2010)

Hi Kev, yes one battery at a time and monitor the battery voltage as well with a volt meter..... if the battery test is ok then I would look at the charging of your solar pannel (at this time of year they are not very good in the uk) and that of the alternater when the engine is running.... but check the batteries first..... thats my view


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## Kev1 (Apr 4, 2011)

Thanks Clive


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## BillCreer (Jan 23, 2010)

Hi Kev,

Are the batteries getting any charge when running on the engine only?


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## rosalan (Aug 24, 2009)

Some car parts shops will do a load test on your batteries for free. I took mine in and they tested them individually; they were ok! That left me with other areas to explore.
It is in the battery suppliers interest to check them for you, they could make a sale.
I know not your van but my batteries are under the drivers seat which made it a bit difficult.
I hope you manage to discover where the problem lies. In my case there were some poor connections that were soon fixed.
Alan


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## spatz1 (May 19, 2011)

you say you ve plugged in overnight and have 300 ah of batteries and reached a voltage of 13.2v in the morning....

most people dont realise although there onboard charger has 20amps written on, this refers to the "stabalised voltage" it can give to run the hab and the sepperate "charger bit" is usually no more than 4amps ......just as my van was.( obviously its not designed to charge 300ah either)

overnight is a max of 16 hours ?? so 4amps x 16hours is only a max of 64ah you ve put into 300ah flat batteries and then had them tested....


I d expect it to need to be on hookup for 3 to 4 days to fully charge 300ah of batteries from the standard 4a charger i ve explained about earlier...

I fitted a fast full 20amp charger for this reason..


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## Kev1 (Apr 4, 2011)

Thanks Alan 
I dropped the batteries off today a t a battery shop to have them load tested
results on Monday

Hi spatz

We have a charger installed under the drivers seat
I have no details on the make etc its just a black box with on off switch.

however
we do have a solar panel and we do have the gene
I would have thought between running them and driving each day it should bump the power up.

See what the results are on the batteries I guess.

Thanks to all again


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## jud (Aug 15, 2009)

Kev1 said:


> We have a Hobby 750
> Fitted with 3 x 100a leisure batteries of varying ages.
> It has an 80w solar panel
> and a generator.
> ...


hi kev1. an 80watt panel will not put much in three 100amp batteries. we have been abroad for 6 weeks and have a 130watt panel going into three 110 batteries and when they have been run down takes some bringing back up to full . running inverters will give your batteries some stick.jud


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## gstringtweaker (Mar 21, 2013)

Hi the testing of batteries is wide and varied, however batteries should be fully charged for at least 48hrs prior to the drop test being carried out.

It must also be noted that batteries of different ages and dissimilar capacities (AH) WILL affect the charging rate. 

This is because batteries over a period of time deteriorate and do lose their internal capacity. So various ages will result in a less effective charge rate.

Also point to note that an 80w solar panel will only kick out 6Amps @ approx 13.4 volts DC. Therefore 2 amp per battery.

Hope this helps

Gstringtweaker


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## DavyS (Jan 10, 2009)

Cant you just fully charge the batteries then switch about 60W of habitation lights on to give a current drain of about 5A. Then time how long before the battery voltage drops below about 12v?
Best if charging and load test done individually for each battery.
Incidentally an old car headlamp bulb, which is about 60W, makes a good load when wired across the battery terminals.


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## dolcefarniente (Jan 2, 2012)

As DavyS says it isn't difficult. Seperate the batteries after fully charging them and stick the same load across each one seperately and meter them every hour or so.If any are faulty the voltage will fall away much quicker. If ok they'll fall in harmony.


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## gstringtweaker (Mar 21, 2013)

*Battery Discharge Testing*

Before any test you must charge any dissimilar aged and also different capacities(shouldn't be fitted together)separate or you will get false readings!
I.E a 100ah battery and an 80ah battery will result in the battery charger charging the 80ah to its maximum possible acceptable capacity and the 100ah to the same as the 80ah.This is due to the battery charger caracteristics as it will see the 80ah as the idealistic value to charge to.

Please do remember batteries have a negative temperature coefficient. Meaning the lower the temp the less output you will get, this is due to the internal battery resistance increasing causing a higher internal battery voltage drop.
Hope this helps.


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## listerdiesel (Aug 3, 2012)

*Re: Battery Discharge Testing*



gstringtweaker said:


> Before any test you must charge any dissimilar aged and also different capacities(shouldn't be fitted together)separate or you will get false readings!
> I.E a 100ah battery and an 80ah battery will result in the battery charger charging the 80ah to its maximum possible acceptable capacity and the 100ah to the same as the 80ah.This is due to the battery charger caracteristics as it will see the 80ah as the idealistic value to charge to.


Not quite correct.

A battery charger will 'see' what it is hooked up to, it doesn't 'know' that the batteries are different sizes and cannot charge one more than the other if they are in parallel.

What 'will' happen is that the battery with the lowest internal impedance will take the most current out of the two, pulling the other battery down to its level if that's how it comes out.

One of the problems with jump starting a car with a flat battery is that the flat one immediately starts dragging the good one down to its level, effectively getting a charge from the better battery.

Charger voltage increases with reduced temperature if the charger has temperature coefficient controls, and on regular daily cyclic charging it isn't a huge amount at our UK temperatures.

Peter


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## gstringtweaker (Mar 21, 2013)

Hi
Nice one Peter? Just change my wording around to say Drags one Battery Down to the other! How can it do this? You stated the battery charger sees what bit sees and can't tell the difference in battery sizes!!??? Make your mind up mate either it can or it can't see battery sizes. As for junp starting vehicles i would recommend (that is ONLY recommend Peter!) Spike arrest jump leads to save spiking the vehicles ECU. Unless you know of some other fandangled device thats bigger and better than mine Peter. LOL


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## Pat-H (Oct 30, 2009)

Sounds like you may have too much battery capacity for your charging abilities.
With all 3 batteries in parallel your voltage won't go up until they all charge so with little sun and limited driving/generator time you could be loosing more than you can put in. Once the voltage drops stuff cuts out.

It maybe better to look at isolating the batteries and switching them over as each dies.

Basically it's possible to split the charge so all three get charged but only 1 battery is available for your load and you then switch over to a fresh one as one gets low. When charging then starts the lowest battery will take more current.

For testing capacity I found an old sealed beam car hedlamp useful. 55W so nearly 6A draw and easy to see when the battery starts to die.
Hook a volt meter across the light connect to battery and start timer.
Note the voltage every hour or 2 and see how the 3 batteries compare.


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