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Discussion Starter #1
I'm not sure if my Leisure battery needs replacing. It's only one and half years old but did run it flat once (albeit for just 12 hours then gave it a good recharge). I've left it alone in the van for a few days and the voltage reads 12.2 V. However, if I put my propex heater on it will gradually creep down to less than 10 V, and then my heater will cut off due to a low voltage error! Any thoughts?
 

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However, if I put my propex heater on it will gradually creep down to less than 10 V, and then my heater will cut off due to a low voltage error!
In rough terms, 12.2V means it's around three quarters discharged already.

You can't infer much from the drop in voltage unless you say how quickly it goes from 12.2V to 10V. If by "gradually" you mean that it takes 2 days, then it may not be in bad shape - if it takes 10 minutes then it's probably shagged.

But if, 30 minutes after you have recharged it with a known good charger, its voltage is around 12.6V, and it's at 12.2V a few days later with nothing connected to it, then it's probably shagged.

If something is connected to it then you can't infer anything unless you know what current it is supplying during those few days.
 

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I'm not sure if my Leisure battery needs replacing. It's only one and half years old but did run it flat once (albeit for just 12 hours then gave it a good recharge). I've left it alone in the van for a few days and the voltage reads 12.2 V. However, if I put my propex heater on it will gradually creep down to less than 10 V, and then my heater will cut off due to a low voltage error! Any thoughts?
To know or not, you really need to give the battery a proper charge so it sits at around 12.8V or so with nothing connected and stays that way for a couple of day. Then use it with a device that draws a known current and see what the battery voltage is after a certain time and do some maths.
I get the impression from your post that the voltages surprise you? It looks like you regard 12.2V as a normal & good battery voltage (it isn't) and that you are surprised 10V is a low voltage (it is).
Campervan and Motorhome systems may be called "12V systems", but in reality, if the battery is at 12V then it really needs good charge and should preferably NOT be used until done so.
 

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Discussion Starter #4
Thanks for the helpful comments both. By gradual, I meant in a few minutes... which is rapid, I guess.

After a good charge I get it to 12.7 V. Have left it overnight (isolated for 20 hours) and it now reads 12.65 V. So some decrease, but not sure what I can infer at this? What other test should I do? How can I do the known current test?! Do I need a special device or can I use, say a fridge, which has a nominal current rating (which I know might not be too accurate).
 

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to do a test you can't really use a fridge as that goes on and off. You need a constant set load. work out the wattage of your lights (and then the current by Current = Watts / Voltage) and leave them on.
A battery capacity is rated based on a "C" value - most are quoted for a C100 value, but some (better) ones use a C20 value. Fro example, what "C 100" means is the capacity quoted in Ah would be supplied if that power was delivered over 100 hours - so for a 100Ah battery, it can deliver 1A for 100 hours (1 x 100 = 100). If it was a C20 rating, it can deliver 5A for 20 hours (5 x 20 = 100). The reason there are different ratings is that the lower the current, the more power can be extracted from a given battery.
Also, you don't get to access all the capacity - you usually don't want to take your batteries below 50% charge - so that 100Ah is 50Ah usable, and can deliver 1A for 50 hours, not 100.
A rough rule of thumb is a battery at 50% charge sits at around 12.05V (different batteries are different, but that is a reasonable number to pick on)

So the test.... if you have a 100Ah battery, fully charge it and then put in a known load (the lights) and leave them on. if they are 12W total = 1A. they should be able to stay on for 50 hours before the battery drops to 12.05V. If the battery drops down to 12.05V in only 25 hours, then your true battery capacity is more like 50Ah (and just 25Ah usable).
If your load is say 5A, then your 100Ah battery should last 10 hours before going down to 12.05V.
treat the time with a 10% leeway, so if it should last 10 hours, but only lasted 9:30 mins, then that is good enough for this test. If it lasted just 5 hours, or even 6 or 7 hours, then that is not good.
 

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Discussion Starter #6
Great advice! My fridge is a Dometic 3 way fridge, which I think when plugged in using the 12V socket draws a constant current? It doesn't go on and off like the compressor fridges. The current is quite high too (8A I think, but will check), which probably caused the battery to get like this in the first place!!!
 

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Discussion Starter #7
One thing I've noticed too, is that my battery terminals loosely rotate - I had assumed this was the design, but I might be wrong. It's a Leoch Xtreme 115 Ah.
 

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My fridge is a Dometic 3 way fridge, which I think when plugged in using the 12V socket draws a constant current?
You don't say what model, but if it's wired full-time to the leisure battery then someone has wired it up wrong! The 12V element on a 3-way fridge is designed only to operate while the engine is running, and there should be a relay to make that happen. As you say, the 12V element has no thermostat, so it's on all the time, unlike the 240V element.

They are intended to be run on either mains or gas while the van is stationary.
 

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Discussion Starter #9
It's the RC1200. No it's not permanently wired up. But I have left it connected to the leisure battery for a couple hours at a time on rare occasions! I admit once I left it connected for 8 hours, but fully recharged the battery 12 hours later.
 

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That's why you need a relay. So it doesn't matter (and you don't trash your battery) if you forget.
 

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Discussion Starter #11
That's why you need a relay. So it doesn't matter (and you don't trash your battery) if you forget.
But at times, I would like to leave it on once stationary. For example, at the beach, where I know I will drive away in a couple of hours and then recharge the battery. I know leaving it on for 8 hours is not recommended and I admit I over did it on that occasion - albeit giving it a good recharge as soon as possible.
 

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That's why it's a 3-way fridge - so you can just switch over to gas in that situation. They are really economical on gas as well.
 

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Discussion Starter #13
That's why it's a 3-way fridge - so you can just switch over to gas in that situation. They are really economical on gas as well.
Yes, I usually run it on gas through my underslung tank. But I have no gas in my van. I don't feel safe running it on gas inside the van, even when it is parked up.
 

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I guess it comes down to what you're comfortable with. I've used 3-way fridges with internal CG/Calor cylinders in camper vans for at least 2 decades - even while sleeping in the van - and I haven't died yet. But there has been a lot of publicity about CO poisoning, so it's understandable that some people don't want to take risks.
 

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The comments about how the 3-way fridge should be wired are correct and really should be used. a Fridge that draws a constant 8A will take a battery down as far as it can safely go on a single afternoon.
If that is ok for the way you use your van (and it may very well be - everyone has different ways to use their vans), then I would strongly recommend you fit a battery protection device that will disconnect the connection when the battery gets below a certain voltage (say below 12.0V is a fair cutoff).
When the battery is "dead" and unable to work say the Fridge or the Heater (you mentioned a figure of under 10V?), that battery is not only discharged, but is physically damaged and if you repeatedly do this, your battery will have an extremely short service life.
 

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Discussion Starter #16
I've done the load test using the fridge as a constant current device. The battery voltage is decreasing steadily at 0.127 Volts per hour. The fridge current is 7.08 Amps. I calculate that the battery has 84.7 Ah at full capacity. It's a 110 Ah battery when new. Does this mean it's knackered or do I just have a lower capacity battery than I used to?! I'm still not sure why my Propex heater was shutting down. It might be that my leisure battery needed a good recharge.

p.s. the 10 V figure is when the Propex was running. If I connected anything of high current, the voltage across the battery dropped from 12.2 to under 10 V. Is it normal for a battery voltage to nosedive when connecting to a device with high cuurent?
 

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The 110Ah will be at a C100 rating almost certainly. The greater the current draw, the less the overall capacity is (a thing called Peukerts Law/Principle). a nominal 110Ah Battery with a constant draw of 8A means you are using the battery at a much greater then C100 and your "110Ah" battery would be lower at that rate of use.
As an example, the Leoch XR1750 AGM battery is a 110Ah Battery at a C100 rating (C100 = drawing 1.1A); when you draw 4.24A constantly, that same 110Ah Battery becomes rated at 92Ah (that is the C20 value); And if you draw 8A constantly on that same battery, the quoted capacity is just 80Ah (the C10 value = 8A x 10 hours).
So if on your test, you are pulling 7A and it looks like it has 85Ah when drawing at that current level, I would say your battery looks pretty decent still. It is just that current is a lot to pull from a single battery that size.
A common reason for a device to shut down due to low voltage when the battery was not actually low is the cabling used is too thin, leading to voltage drop. This is very common with Compressor Fridges and Diesel Heaters. Not sure about Propex.
 
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