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pearley

Battery Capacity & Temperature

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The last four winters, during the worst of the weather we were on a shoreline so I can't remember how my batteries behave in the cold weather. We are gas free so the batteries during the day are always fairly well charged but I notice that they drop off badly overnight. I can go to bed with a SOC of 85-90% with a warm engine bay due to the generator being run and wake up in the morning with the Smartguage showing about 65% Reading of the effect of temperature on battery capacity it suggests a reduction of 20% at freezing. Given that the batteries sit on the swim and the canal is frozen, I suppose that the battery temperature can't be far from zero.

 

When this first started happening about 2 weeks ago I thought that my batteries were on the way out - they are nearly 3 years old - but then I can leave them during the day for several hours without the SOC altering so perhaps they'll stagger on until the Spring.

 

Any one tried insulating under and around the batteries and would it work anyway?

 

Regards

Pete

Edited by pearley

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The last four winters, during the worst of the weather we were on a shoreline so I can't remember how my batteries behave in the cold weather. We are gas free so the batteries during the day are always fairly well charged but I notice that they drop off badly overnight. I can go to bed with a SOC of 85-90% with a warm engine bay due to the generator being run and wake up in the morning with the Smartguage showing about 65% Reading of the effect of temperature on battery capacity it suggests a reduction of 20% at freezing. Given that the batteries sit on the swim and the canal is frozen, I suppose that the battery temperature can't be far from zero.

 

When this first started happening about 2 weeks ago I thought that my batteries were on the way out - they are nearly 3 years old - but then I can leave them during the day for several hours without the SOC altering so perhaps they stagger on until the Spring.

 

Any one tried insulating under and around the batteries and would it work anyway?

 

Regards

Pete

 

Temperature DOES (negatively) affect wet-cell batteries (Linky)

 

And insulation from cold certainly would do no harm - it could only help in principle

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Yes, I found a couple of sections of insulation floating in the cut, from a careless boat fitter probably, quite large pieces. And I thought at the time it would be a good idea to use it to insulate the batteries :)

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They don't lose actual capacity at low temperatures. The delivery mechanism slows down (the chemical reactions are slower) so that under load they appear to go flat quicker. At very low temperatures, even tiny loads can make them apparently flat much quicker than in summer.

 

Think Peukert, and that the effect gets worse as the temperature drops.

 

PS. And yes, keeping them warm will help.

Edited by Gibbo

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Yes, I found a couple of sections of insulation floating in the cut, from a careless boat fitter probably, quite large pieces. And I thought at the time it would be a good idea to use it to insulate the batteries :)

 

I used to have an old Mini many years ago which of course had the batteries in the boot well away from the engine. We used to insulate the battery box and top with polystyrene foam and it did deem to help keep them going during very cold spells.

 

I suppose there was a possible fire risk to this but didn't consider that when young and daft.

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I can't believe how cruel some people are to their batts, ours are tucked up comfortabely in the back cabin sat on 18mm ply and 50mm of polyurethane insulation. I couldn'sleep at night if they were shivering in the engine bay.

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They can generally be charged at a higher voltage when cold, some chargers and alt controllers do this with a sensor. Also 'wet' batts sitting on a cold surface may tend to stratify more, especially if not fully charged that often.

 

cheers, Pete.

~smpt~

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I can't believe how cruel some people are to their batts, ours are tucked up comfortabely in the back cabin sat on 18mm ply and 50mm of polyurethane insulation. I couldn'sleep at night if they were shivering in the engine bay.

Hopefully this kind treatment will ensure that they are never inconsiderate enough to explode when you are on board. :rolleyes:

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You could always just extend their cables, take em to bed and cuddle up to em to keep them warm. Ooh and keep a night light burning in case they're afraid of the dark.

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Insulating your batteries may help to reduce the rate at which their temperature begins to fall during the evening. However, unless the batteries have some sort of heat source, then over the course of a night I very much doubt you'd see a lot of difference between the temperatures of insulated and uninsulated batteries.

 

It's a bit like people who seem to think that just insulating a cold pipe will stop it from freezing. It may retard the temperature drop, but eventually the pipe will freeze because heat always flows spontaneously from regions of higher temperature to regions of lower temperature, and never the reverse, unless external work is performed on the system.

 

For boats connected to shore power I imagine the battery charger acts as a small heat source. I don't know if a battery which isn't being charged produces a small amount of independent heat from chemical changes within it? If so, then this is the heat which should be insulated. Without some "external work" all attempts to insulate the batteries will be useless.

Edited by blackrose

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They don't lose actual capacity at low temperatures. The delivery mechanism slows down (the chemical reactions are slower) so that under load they appear to go flat quicker. At very low temperatures, even tiny loads can make them apparently flat much quicker than in summer.

 

Think Peukert, and that the effect gets worse as the temperature drops.

 

PS. And yes, keeping them warm will help.

But remove the insulation in warmer weather so when charging and discharging they do not overheat?

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But remove the insulation in warmer weather so when charging and discharging they do not overheat?

 

Indeed.

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I remember reading somewhere that batteries self discharge slower at lower temperatures, thus requiring less frequent re-charging (if not being used of course).

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I remember reading somewhere that batteries self discharge slower at lower temperatures, thus requiring less frequent re-charging (if not being used of course).

 

Correct.

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Modern lead acid batteries work best at about 20C. Above this performance improves but life decreases dramatically, below this there is a temporary reduction of current supply til the cells warm up. There is something to be said for insulation, putting the batteries in a warm place or even heating them in winter.

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More decisions,

 

cassette or pump out, now to insulate or not.

 

COAT!!

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Modern lead acid batteries <snip> There is something to be said for insulation, putting the batteries in a warm place or even heating them in winter.

What sort of blow lamp would you recommend? Alternatively, is there an electric heater that could be connected to the battery?

 

(No need to get hat and coat - already wearing it!)

 

Seriously, what did you have in mind when you said heating them in winter? I was wondering if anyone had produced a hot water bottle for batteries - the gas hob could heat the water.

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