How can you tell

[Bosunof]

I've got three batteries, one for engine starting and two for domestics. How do I tell whether they are still fully serviceable and can be used for the next season. I dont have any electrical apparatus but need to know what to replace.

Thanks for any simple suggestions that dont finish up with me getting a serious injury.

 

[rob2]

The only sure way I know of is to start buying drinks for automotive electricians until you find one with a drop tester. I had a friend who used to work for Lucas, who tested mine. The nominal figures for the battery when new are dialled into the tester which is then put across the terminals. The voltage drop against time (only about 30 secs) is used to calculate the state of charge and remaining capacity of the battery.

Rob.

 

[VicS]

Charge them with a good multi-stage charger.

If you cannot get them to a stage where the voltage is 12.7 ish or more after resting ( no load no charging) for 24 hours ... probably not much good.

Monitor the volts for a period. If they dont stay up to around 12.6 after a couple of weeks doing nothing they are probably not going to hold a good charge.

If they are not sealed check the electrolyte densities ... but not just after topping up. If there is a significant difference between the cells it's probably a sign that they may not last much longer.

Finally get them professionally tested. In particular a "drop test" for the starter battery.

 

[Plevier]

The only sure way I know of is to start buying drinks for automotive electricians until you find one with a drop tester. I had a friend who used to work for Lucas, who tested mine. The nominal figures for the battery when new are dialled into the tester which is then put across the terminals. The voltage drop against time (only about 30 secs) is used to calculate the state of charge and remaining capacity of the battery.

Rob.

This is only valid for a vehicle starter battery. It will give a good idea of the cranking capability and an idea of the reserve capacity, this is the length of time for which it will supply 25 amps.
The only reliable way of capacity checking batteries for low rate discharge capacity i.e. against the nominal Ah capacity is by doing a real discharge test over at least 8 hours.
Doing it accurately is not easy but you can get a working idea by using bulbs.

 

[john_morris_uk]

The only sure way I know of is to start buying drinks for automotive electricians until you find one with a drop tester. I had a friend who used to work for Lucas, who tested mine. The nominal figures for the battery when new are dialled into the tester which is then put across the terminals. The voltage drop against time (only about 30 secs) is used to calculate the state of charge and remaining capacity of the battery.

Rob.

Drop testers are good for starter batteries, but I am very anxious that people should suggest that they are the correct way of checking a deep discharge traction or leisure battery. Leisure batteries are NOT designed for the cold cranking currents used by a drop tester. You might even damage the battery by using such a devise on them.

If the domestic batteries are deep discharge ones, then the only really effective way of testing them are to charge them up and do a measured discharge over a number of hours, and then re-charge them straight away to avoid sulphation and damage. There are various ways to do this and a bit of research will give you a number of techniques together with details for even the most elementary of battery and boat electric bods.

Edit: Just noticed that SWMO came home in the middle of my typing my response and by the time I finished my typing after supper, someone else has already said much the same thing!

 

[Plevier]

Drop testers are good for starter batteries, but I am very anxious that people should suggest that they are the correct way of checking a deep discharge traction or leisure battery. Leisure batteries are NOT designed for the cold cranking currents used by a drop tester. You might even damage the battery by using such a devise on them.

Damage is pretty unlikely, but what I didn't think of adding in my previous post is that a serviceable leisure battery could give you a false fail on this sort of tester because of its limited high rate capability. Not probable but possible.

 

[rob2]

Ok, I stand corrected. I find some of the new battery technology can be confusing, especially as some suppliers seem reluctant to identify exactly what type of battery they are supplying (especially the cheaper leisure types). If you're spending vast amounts on very deep discharge batteries, then the test may not be relaible.

Just to clarify, my batteries are old, around 100 Ah nominal and also quote a CCA rating. Does that make them semi-traction type? The tester used was programmed with both figures and reported both the state of charge and the actual capacity of the battery. One was reported as around 90% capacity but in need of charging, the other was basically condemned as low capacity. Both are still in service although I use the better one for starting.

Rob.

 

[EdWingfield]

Visit your local RNLI. Ask the engineer who he uses - he will be knowledgeable and reputable.

You are most likely to get an honest appraisal, as I did. He said he could sell me a new battery but it'd be no better than the one I had.

 

[fisherman]

I was told to use a hydrometer, if any cell was noticeably down on the others, charged or discharged, it would be duff.

 

[Icarus39]

I have 1 engine starter battery - proper cranking battery as used on Mercs, big audi's, etc. So long as I know that one is A1 and isolated from the service bank, then it's no great shakes if I were to suddenly discover the service bank is problematic and due replacement. I can still start the engine and get things charging !
For me, the engine starter battery - replace at least every 3 years - only cheap really at 75 quid (25 a year).
The service bank is properly charged so should last me 5 years as they are well maintained / charged. By then I should have a pretty good idea how good they are from normal use, etc.

I wouldn't worry too much about defining exactly the state of your service bank / batteries ... just make sure your engine starter battery is 100% at tall times - change it before you start to doubt it ...

 

[ghostlymoron]

I have 1 engine starter battery - proper cranking battery as used on Mercs, big audi's, etc. So long as I know that one is A1 and isolated from the service bank, then it's no great shakes if I were to suddenly discover the service bank is problematic and due replacement. I can still start the engine and get things charging !
For me, the engine starter battery - replace at least every 3 years - only cheap really at 75 quid (25 a year).
The service bank is properly charged so should last me 5 years as they are well maintained / charged. By then I should have a pretty good idea how good they are from normal use, etc.

I wouldn't worry too much about defining exactly the state of your service bank / batteries ... just make sure your engine starter battery is 100% at tall times - change it before you start to doubt it ...

3 years is not long for a battery that has such an easy life - it should last upto 10.

 

[Plevier]

Ok, I stand corrected. I find some of the new battery technology can be confusing, especially as some suppliers seem reluctant to identify exactly what type of battery they are supplying (especially the cheaper leisure types). If you're spending vast amounts on very deep discharge batteries, then the test may not be relaible.

Just to clarify, my batteries are old, around 100 Ah nominal and also quote a CCA rating. Does that make them semi-traction type? The tester used was programmed with both figures and reported both the state of charge and the actual capacity of the battery. One was reported as around 90% capacity but in need of charging, the other was basically condemned as low capacity. Both are still in service although I use the better one for starting.

Rob.

It's nothing to do with new battery technology.
Putting it VERY crudely, what you suggested is a little bit like running an engine at full power, measuring the fuel flow rate and using that times a generic fudge factor to predict how long a tankful will last at low power!
Yes there are all sorts of technical invalidities in that comparison but does it give you a feel for what I mean?
You can really only check low rate endurance of a battery with a low rate endurance test.

The fact that your batteries have CCA ratings shows that they are OK as starter batteries i.e. they are not restricted to low rate discharges. "Semi-traction" or "leisure" doesn't actually mean anything specific in the industry. It may indicate that they have thicker plates than that manufacturer would use in a pure starter battery, but on truck size batteries i.e. 100Ah and over - roughly, not a rigid definition - probably the same typically 4mm, and/or heavier separators between the plates, maybe a layer of glass mat as well as the normal microporous PVC, and the plates may be in pockets.
Compare with a car starter battery that usually has plates 1-2mm thick and single PVC separators; a flat plate traction battery for fork lifts, milk floats etc that might have 6-8mm thick plates and multiple separation; and the ultimate cyclic/traction construction the tubular plate, paste held in rows of tight nylon tubes maybe 1cm dia with a lead spine in the middle. Difficult to describe. Heavy, big, expensive, not high rate, but very long cycle life.

You could run a very rough test on your "failed" battery - a 60W headlamp bulb should run for about 20 hours at 20 deg C from it to a final on-load voltage of about 10.5V if it's giving 100%. (You should never go this low in normal service, this purely for a test. Recharge immediately.)

This test will only mean anything if you can get the battery really fully charged just before it - a 14.5-15V boost for a few hours, not just 13.8V float. I note your auto tester said one needed charging - I suggest it can't hope to make valid measurements with a battery in that state.

In a critical application you would normally scrap a battery as potentially unreliable if less than 80% capacity. Just empirical, no theory behind it that I know of.

If your "failed" one still starts the engine vigorously (as it's much bigger than you need unless you have a big engine), you might be better using it for that and the "good" one for your domestics.

 

[Plevier]

3 years is not long for a battery that has such an easy life - it should last upto 10.

+1
About 20 years ago the UK average figure for cars was that the battery would fail in its 5th winter. (It's the summer that does the damage but the winter shows it up - all the cars stuck at the roadside with the first frost!) I believe with improved battery and alternator quality it's now 6 years.
Lots of people with boats get longer life because we use vastly oversized batteries compared with cars giving more degradation tolerance and we don't use them much.
There's something wrong if you have to replace 3 yearly, if it's only doing starting, not being deep cycled.

 

[Icarus39]

+1
About 20 years ago the UK average figure for cars was that the battery would fail in its 5th winter. (It's the summer that does the damage but the winter shows it up - all the cars stuck at the roadside with the first frost!) I believe with improved battery and alternator quality it's now 6 years.
Lots of people with boats get longer life because we use vastly oversized batteries compared with cars giving more degradation tolerance and we don't use them much.
There's something wrong if you have to replace 3 yearly, if it's only doing starting, not being deep cycled.

Maybe 3 years is pessimistic, but I certainly wouldn't head off to sea with an engine started battery that is more than 5 years old. I think you are missing my point that for 75 quid every few years you can have 100% peace of mind that you can always start your engine and charge .... I'd hate to be out at sea, have a diesel problem, have to bleed the diesel ... doesn't start easily and my 10 year old battery gives up the ghost ... all for saving a few quid ?

For me, 5 years absolute max for the engine starter .. small price for big peace of mind.

 

[Plevier]

Maybe 3 years is pessimistic, but I certainly wouldn't head off to sea with an engine started battery that is more than 5 years old. I think you are missing my point that for 75 quid every few years you can have 100% peace of mind that you can always start your engine and charge .... I'd hate to be out at sea, have a diesel problem, have to bleed the diesel ... doesn't start easily and my 10 year old battery gives up the ghost ... all for saving a few quid ?

For me, 5 years absolute max for the engine starter .. small price for big peace of mind.

Yes I do see your point. I think 3 years is hyper cautious but I would certainly be nervous with a 10 year old one!

 

[William_H]

Batteries

You worry too much. You have a duplicated power system to give redundancy in case of battery discharge or failure. This is far more than you have in your car Which might be more critical to you.
Do the double domesticated batteries do the job you want? try separating them and check out actual use performance as individuals. ie will they run lights for many hours without going flat.
Presumably the engine start battery will start the engine. Now can you try starting the engine with any one of the domestic batteries? If not that battery is no good to you. But you could risk it on the basis that you would start using both domestic in parallel if the engine battery were dead.
In the end you will know when and if a battery is no good. It will tell you so don't worry... olewill

 

[Bosunof]

Thank you all. Good notes and I will get to it as soon as I have got the old girl under cover. To all who have a boat... happy refitting oooh and yes, an inexpensive one too.