# Testing Battery Life



## IanA (Oct 30, 2010)

Is there a way of testing my leisure battery life without spending hours waiting for it to run down? I know I can switch on all the lights, heating etc, but this will give an artificially high load which may give a false reading. I can see the battery voltage on my control panel, but how would I measure current? I have multimeter but not sure where to connect it.

Also - on my charger I have two switches - one marked charger, one marked heater. The charger is straightforward, turn it on and the battery starts charging and the 12v lights get a bit brighter. The heater one is different - the gas-powered heater works regardless of the switch position and I don't think the MH has an electric heater. Any ideas?
Thanx


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## CliveMott (Mar 10, 2008)

On 1 the answer is no. The only accurate to test the batteries actual capacity is to do a discharge test.

For me I hang a spare headlight bulb across the battery as well as a digital voltmeter and measure the number of hours it takes for the voltage to fall to 11 volts. The bulb current I also record at invervals so I can accurately quantify ampere-hours . Average current around 4.5 amps.

2 Dunno. sorry
C.


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## pieterv (Feb 3, 2009)

Note though, that discharging to 11V is a very deep discharge, which won't do the battery any good, so don't do it too often.


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## clive1821 (Mar 27, 2010)

I agree with my name sake... the only way to test a battery is to load test it, for example my new 110AH battery I tested last week before installing it, simple and crude way, my inverter connected to a mains lights (150 Watt) which is about 15 amps with the extra current taken by the inverter say total load about 18amps... and the light stayed going for just over 5 hours, which is a good indication of the battery working ok, I made it 75% efficient which is not to bad, my faulty battery lasted 15minutes under the same test, and its was showing fully charged as well at 13.8 volts + My view is a good practical test like this gives you a the best idea....


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## sallytrafic (Jan 17, 2006)

I too use a 60W headlamp. I plot the voltage against time on a graph and stop discharging as soon as the slope of the graph dramatically increases 
Here's one I left too long


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## wakk44 (Jun 15, 2006)

I agree the only way to test a battery properly is a constant load test,the only problem with this method though is that we are constantly told not to let a leisure battery drop below 50% state of charge to avoid long term damage.

The recent thread about Elecsol batteries and trying to claim on their warranty illustrated how difficult it was to get a full written report on an alleged faulty battery.


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## CPW2007 (Aug 17, 2007)

IanA said:


> Is there a way of testing my leisure battery life without spending hours waiting for it to run down? I know I can switch on all the lights, heating etc, but this will give an artificially high load which may give a false reading. I can see the battery voltage on my control panel, but how would I measure current? I have multimeter but not sure where to connect it.
> 
> Also - on my charger I have two switches - one marked charger, one marked heater. The charger is straightforward, turn it on and the battery starts charging and the 12v lights get a bit brighter. The heater one is different - the gas-powered heater works regardless of the switch position and I don't think the MH has an electric heater. Any ideas?
> Thanx


Hi, with regard to the heater switch; on the EC200 in our motorhome, the (green) heater switch operates the heating element within the Trumatic water heater (only when on hook-up), the switch illuminates when operated. When on hook up, we normally use both the electric and gas to quickly heat up the water and then just use electric for the duration of the stay on the site. Actual heating of the m/home is gas heated blown air only, we have no electric heating as such.

Regards

Chris


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## clive1821 (Mar 27, 2010)

Ha ok I did not understand your 2nd question and yes aggree with chris, the truma c6002el has a 240v electric heater and that green switch lights up when switched on when conected to the mains supply.


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## trevorf (May 16, 2005)

I use one of these 

battery load tester

Trevor


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## clive1821 (Mar 27, 2010)

Trevor as you have use this unit how exactley do you use it? dose it just look at the IR and Volts?


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## trevorf (May 16, 2005)

Hi Clive

Not 100% sure of the exact technicalities but it is a digital load tester.
You select the battery type, approx CCA (cold cranking amps) and then hit the test button.
As far as I know it puts a high load on the battery for a very short period of time then gives a reading in CCA. 
As far as I know CCA is a measurement of the batteries power equivalent to engine torque.
Maybe someone like Clive Mott, Dave Burleigh or Frank(sallytraffic) could give us a more technical answer.




Trevor


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## erneboy (Feb 8, 2007)

Clive download the instructions here: http://www.justoffbase.co.uk/Digital-Battery-Tester-12V-Sealey-BT2101

This one can be used on batteries of up to 120ah capacity which is what I want. Be careful you buy the right one, some will not work with such big batteries. I don't know why. Also I think I am correct in saying that leisure batteries may not (even possibly should not) give a CCA rating as they are not designed for cold cranking, Alan.


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## clive1821 (Mar 27, 2010)

Thanks Trevor, and Alan,

Yes its not quite the item to use when you are doing a load test, its far better to a 5 hour load test as described above, a constant load of from 4 to 15 amps will be fine.... the load tester is also a useful guide for a quick test, when an untrained person needs a go no go tester... in my view if we need a battery life test its just a better way of testing using a simple tester a constant load and do a real check in real life, as we need current at a constant time for a long as well can get, and not just a cold crank time... be interested in other views..


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## erneboy (Feb 8, 2007)

Thanks Clive. Not having much understanding of electricity or batteries I would not know but surely this must give a fairly reliable reading. Of course it will not give the exact capacity which the longer test running down to 11 volts would.

Do the experts think it is so unreliable as to not be worth having or at least not good enough to depend on? Alan.


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## clive1821 (Mar 27, 2010)

Alan,

I have just bourght one and I'll report on ite function and let you know by the end of the week ...


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## IanA (Oct 30, 2010)

Thanks for all the info - I had a little dabble at the weekend - it was freezing cold so I put the heater on - gas, no water. The leisure battery started at 12.5v but dropped as the fan started - with fan at full speed the voltage was fluctuating between 11.3 and 11.5v after about 15 minutes but returned to 12.4 when I turned the heater off. I restarted the heater and it did the same. Then my wife told me it was time to go home.....

More testing needed, but I was thinking that a second leisure battery seemed to be the best way forward for extended use - eventually I think I'll go solar but can't afford it just yet.


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## erneboy (Feb 8, 2007)

Ian solar won't do anything worthwhile at this time of year, Alan.


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## clive1821 (Mar 27, 2010)

Hi Ian, well thats good that you tried, from the figures you gave, would lead me to believe that the battery is undercharged, would be an idea charge the battery up and then do the same test... if its the trauma main fan it should not take much current... looking forward to hearing how you get on... as far as the solar panels I agree with Alan, they will give out very little current this time of year, just enough to keep the battery maintained with the standing current of the alarms and other 24/7 equipment on the van... the very south of Spain might be a different story...


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## clive1821 (Mar 27, 2010)

Further report, I have received the Sealey battery tester and I confirm that this test is not good and not worth relying on the testers results, as it did not shower up the fault up I have on this battery, but the simple load test is by far the better test, and shows up the fault within 15 minutes... that's my first hand findings.


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## erneboy (Feb 8, 2007)

Thanks for the info. Clive I will make a tester of my own then, Alan.


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## ramblingon (Jul 15, 2009)

For the ladies -Drive to Halfords they will test it for free. :roll:


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## erneboy (Feb 8, 2007)

And the result may well not be accurate Ladies! Alan.


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## Ken38 (Mar 24, 2009)

A subject still dear to my heart!

The only real test for capacity is to run the battery down with a known current but don't take it past 50% charge, 25% at the very most. They don't like it!

Halfords and most battery suppliers will tell you the batteries charge state and if it can supply enough current to start a vehicle. Those are different to Amp.Hour capacity.

The attached table gives details of % charge versus voltage but remember they are open circuit voltages. Check the voltage immediately you remove the load, otherwise you get a higher reading due to surface charge.

I found http://www.batterystuff.com/tutorial_battery.html really useful.

Really try not to run a battery flat. It really causes them to lose Amp.Hour capacity quickly.

A better test of charge is a hydrometer. You may be able to borrow one but be careful, battery acid is not kind to most things.

So a rough test. Charge the battery. Check its voltage or Specific gravity. Connect a 60W lamp for four hours. Recheck the voltage of specific gravity.

You will have taken approx 5A x 4hrs out (20 AH). If the battery is still 60% charged then its capacity is approx. 50AH (20 / 40 * 100).

Good luck.


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## clive1821 (Mar 27, 2010)

Yes as I first mentioned my view is to do a real simple test, I used an inverter and loaded it with a 100 watt lamp and let it run until the inverter closed down... simple but very informative, my faulty battery lasted 15minutes, a good battery lasted about 5.5 hours so i'm happy about the good battery. The tester just said both batteries were good... there's an object lesson.


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