Slinky Spring
Member
How do you test leisure batteries? Is it the same drop test as a normal battery or does that not work.
Testing leisure batteries
- Thread starter Slinky Spring
- Start date
john_morris_uk
Well-known member
A drop test would be the wrong test.
Leisure batteries are designed to withstand longer periods of slow discharge. A drop test simulates cold cranking current and measures the voltage across the battery under these extreme conditions. Some leisure batteries may be damaged by such extreme treatment.
The best way to test would be to ensure the battery is charged fully and then discharge it over a period of several hours into a known load (say a couple of car headlamp bulbs) Ideally monitor the specific gravity or if you can't do that monitor the voltage with an accurate voltmeter. When it gets down to 11.7 volts or so you will know that the battery is flat. Recharge immediately. If you leave it totally discharged then you will damage the battery.
If you multiply the current drawn by the headlamps by the number of hours it takes to discharge the battery, then you have the total Amp-hours capacity of the battery. If you don't want to risk damage by totally discharging the battery then discharge until the voltage is 12.2 volts or the specific gravity is 1.190 which is half charge.
Most experts advise not discharging the battery more then 50% anyway because if you only discharge to 50% then you dramatically increase the life of your battery.
Leisure batteries are designed to withstand longer periods of slow discharge. A drop test simulates cold cranking current and measures the voltage across the battery under these extreme conditions. Some leisure batteries may be damaged by such extreme treatment.
The best way to test would be to ensure the battery is charged fully and then discharge it over a period of several hours into a known load (say a couple of car headlamp bulbs) Ideally monitor the specific gravity or if you can't do that monitor the voltage with an accurate voltmeter. When it gets down to 11.7 volts or so you will know that the battery is flat. Recharge immediately. If you leave it totally discharged then you will damage the battery.
If you multiply the current drawn by the headlamps by the number of hours it takes to discharge the battery, then you have the total Amp-hours capacity of the battery. If you don't want to risk damage by totally discharging the battery then discharge until the voltage is 12.2 volts or the specific gravity is 1.190 which is half charge.
Most experts advise not discharging the battery more then 50% anyway because if you only discharge to 50% then you dramatically increase the life of your battery.
VicS
Well-known member
[ QUOTE ]
then you have the total Amp-hours capacity of the battery
[/ QUOTE ] Ah but the capacity of a battery is quoted at a specific discharge rate eg 20 hour rate. So the load should be chosen so that the battery is discharged iover that time, not vastly quicker or slower.
That means that a 60Ah battery should be discharged at as close to 3 amps as reasonably possible or a 90Ah one at 4.5 amps etc. A <u>single</u> car headlamp bulb will be about right for a 90Ah battery but a bit much for a 60Ah one and not really quite enough for a 90Ah one.
The actual current ought to be checked periodically to determine an average figure to use for the final calculation.
Without all this trouble you'll get a good indication of the state of the battery by charging it and then monitoring either its specific gravity or the no load volts over a period of several weeks.
I like to charge until I get a rested voltage reading of at least 12.7 volts and then monitor that for up to a month. Although it will fall fairly quickly at first a good battery will be falling very slowly at about 12.6 v after 3 or 4 weeks.
then you have the total Amp-hours capacity of the battery
[/ QUOTE ] Ah but the capacity of a battery is quoted at a specific discharge rate eg 20 hour rate. So the load should be chosen so that the battery is discharged iover that time, not vastly quicker or slower.
That means that a 60Ah battery should be discharged at as close to 3 amps as reasonably possible or a 90Ah one at 4.5 amps etc. A <u>single</u> car headlamp bulb will be about right for a 90Ah battery but a bit much for a 60Ah one and not really quite enough for a 90Ah one.
The actual current ought to be checked periodically to determine an average figure to use for the final calculation.
Without all this trouble you'll get a good indication of the state of the battery by charging it and then monitoring either its specific gravity or the no load volts over a period of several weeks.
I like to charge until I get a rested voltage reading of at least 12.7 volts and then monitor that for up to a month. Although it will fall fairly quickly at first a good battery will be falling very slowly at about 12.6 v after 3 or 4 weeks.
john_morris_uk
Well-known member
[ QUOTE ]
Ah but the capacity of a battery is quoted at a specific discharge rate eg 20 hour rate. So the load should be chosen so that the battery is discharged iover that time, not vastly quicker or slower.
[/ QUOTE ]I agree - but my simple answer was getting more and more complicated so I thought I'd miss out the 'at that discharge rate' bit. I am not so sure that the self discharge rate (which appears to be what you are suggesting) is the best way to measure the capacity of a battery?
Ah but the capacity of a battery is quoted at a specific discharge rate eg 20 hour rate. So the load should be chosen so that the battery is discharged iover that time, not vastly quicker or slower.
[/ QUOTE ]I agree - but my simple answer was getting more and more complicated so I thought I'd miss out the 'at that discharge rate' bit. I am not so sure that the self discharge rate (which appears to be what you are suggesting) is the best way to measure the capacity of a battery?
VicS
Well-known member
[ QUOTE ]
I am not so sure that the self discharge rate (which appears to be what you are suggesting) is the best way to measure the capacity of a battery?
[/ QUOTE ] No I am not suggesting it as way of measuring the capacity, what you suggest is the way to do that, but it will give an indication of how well the battery is going to hold a charge. It'll not be much good if it's capacity is good but it doesn't hold the charge for more than a few days. Marginally more useful if the capacity is down but capable of holding it. Internal resistance is another thing but while very important for a starter battery not so critical for a "domestics" battery.
I am not so sure that the self discharge rate (which appears to be what you are suggesting) is the best way to measure the capacity of a battery?
[/ QUOTE ] No I am not suggesting it as way of measuring the capacity, what you suggest is the way to do that, but it will give an indication of how well the battery is going to hold a charge. It'll not be much good if it's capacity is good but it doesn't hold the charge for more than a few days. Marginally more useful if the capacity is down but capable of holding it. Internal resistance is another thing but while very important for a starter battery not so critical for a "domestics" battery.
nedmin
Active member
The way I find if there U/S is that if there more than about 4yrs old and you think they are knackered they usually are.Over many years I,ve tried reverse charging, additives etc ,but at the end of the day its throw away time.
alan
Active member
I have used the method desribed on the "Voltwatch" web site. This involves discharging at the 20 hour rate and discharging them to 50% whilst monitoring the volts regularly ( I use a voltmeter with a program on my PC). The discharge is reasonably linear after the first hour. The only problem I have with the method described on the above web site is that all the measurements are made on-load and thus are "pessimistic". If you take the battery off-load for about ten minutes (should be longer really, but is a compromise for practicallity) and then make the voltage measurements you will get a more realistic result. This method works quite well and does give you an idea if the batteries are cream-crackered or not. I have just replaced two 70 Ah batteries because the result of this test indicated that they only had about 35Ah .... I already really knew this because when I was anchored for a few days last summer I could tell that they were good as before.
As these batteries are only two years old I am at present de-sulphating them with a Curtiestown de-sulphator to see (a.) if de-sulphitisation works (b,) if I can recover these batteries for oither uses.
Alan,
As these batteries are only two years old I am at present de-sulphating them with a Curtiestown de-sulphator to see (a.) if de-sulphitisation works (b,) if I can recover these batteries for oither uses.
Alan,
William_H
Well-known member
I would question the worth of testing a leisure battery. If you do test it and can get 50% of the published rating out of it , it is probably pretty good.
In service you will know if a battery is not doing the job you want. ie it seems to go flat quickly compared to last season. I would reckon that batteries when wired in parallel should be seperated and used seperately at least occasionally to ensure that both batteries are OK.
If this question comes as a desire to have a boat fully reconditioned for the new season then don't bother about the batteries they will die when they are ready. That is the time to replace them. olewill
In service you will know if a battery is not doing the job you want. ie it seems to go flat quickly compared to last season. I would reckon that batteries when wired in parallel should be seperated and used seperately at least occasionally to ensure that both batteries are OK.
If this question comes as a desire to have a boat fully reconditioned for the new season then don't bother about the batteries they will die when they are ready. That is the time to replace them. olewill
john_morris_uk
Well-known member
[ QUOTE ]
[ QUOTE ]
I am not so sure that the self discharge rate (which appears to be what you are suggesting) is the best way to measure the capacity of a battery?
[/ QUOTE ] No I am not suggesting it as way of measuring the capacity, what you suggest is the way to do that, but it will give an indication of how well the battery is going to hold a charge. It'll not be much good if it's capacity is good but it doesn't hold the charge for more than a few days. Marginally more useful if the capacity is down but capable of holding it. Internal resistance is another thing but while very important for a starter battery not so critical for a "domestics" battery.
[/ QUOTE ]Fair enough and I wasn't sure you really meant that either, but wasn't sure of the logic behind what you were suggesting. The ability of a battery to hold charge is a much ignored facet of the powergeneration-battery-useage triangle.
[ QUOTE ]
I am not so sure that the self discharge rate (which appears to be what you are suggesting) is the best way to measure the capacity of a battery?
[/ QUOTE ] No I am not suggesting it as way of measuring the capacity, what you suggest is the way to do that, but it will give an indication of how well the battery is going to hold a charge. It'll not be much good if it's capacity is good but it doesn't hold the charge for more than a few days. Marginally more useful if the capacity is down but capable of holding it. Internal resistance is another thing but while very important for a starter battery not so critical for a "domestics" battery.
[/ QUOTE ]Fair enough and I wasn't sure you really meant that either, but wasn't sure of the logic behind what you were suggesting. The ability of a battery to hold charge is a much ignored facet of the powergeneration-battery-useage triangle.
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