AGM batteries - how reliable is CCA testing?

[KompetentKrew]

During the pre-purchase survey of my boat the surveyor condemned the entire battery bank, both house and starter.

2 x 165 AGM, Port battery 265 CCA EN replace, Sb 765 CCA EN.
As these are in parallel, both need to be replaced. Check that the wiring of the charging is mounted correctly, + on one battery, - on the other.
Starter battery 325, replace.

He attributes this to the Victron inverter / charger, which must be at least 10 or 15 years old and which he reckons is under-reading the voltage - I haven't had a chance yet to check this myself, but he speculates it's therefore been overcharging the batteries and this is what killed them, which does make sense.

The PO is astonished by this discovery, as he's never had any problems with any of them. The starter battery turns the engine over fine, and he remarks that the AGMs are only 3 years old and these should last 10. Well, I suppose that doesn't account for overcharging them.

The surveyor tested the batteries with a Novitec battery tester - I do not know the exact model.

I have tested the house bank simply by isolating each of them in turn - to within 1% or 2% each shows 13.9v, although I guess I should have allowed them time to rest after disconnecting them from the solar panels. I'm not used to AGM batteries, and this is much higher than my van's battery, but I gather it is normal or good for AGMs.

Is it possible the surveyor could be wrong about the condition of these batteries, or should I just accept he has better tools than me?

One thing I did notice is that multiple negative leads are connected to the same post, and that the thickness of their barrels prevents the bolt from being properly tightened. There is a wedge-shaped air gap between them. I don't see how this can have affected the battery testing as the surveyor isolated the batteries to retest them after the PO voiced his surprise. It has just occurred to me, as I write now, that this could be what's causing the charger to under-read the voltage. Thoughts?

As always, I appreciate the forum's time and help.

 

[matthewriches]

Oh such a shame to have such nice batteries to then attach such crap connections to!

It would be advantageous to instruct a qualified electrician to carry out some testing as part of any negotiation, unless of course your surveyor is such?

Very simply put (at 3.30am in the morning), the only real way to test a battery properly is to disconnect, allow to settle and apply a known load over a sustained period. Calculations can then be made and conclusions drawn as to the health of each individual battery.

 

[wipe_out]

As mentioned above you have terrible connections there and they don't have the full surface area to make contact..

I would test the batteries by removing them then fully charging them and let them stand to see how much they drop voltage over about a week.. Then you could take them to a car battery place where they can plug on their load tester to check what CCA they are capable of.. This is pretty basic testing but should point you in the right direction.. They may not be 100% but may still have plenty life left in them..

If they are are in parallel and one is bad then you will need to replace both.. Replacing just one is never a good idea..

I have just been through the process of completely rewiring our (new to us) boat for everything before the battery switch because it was a mess with terrible connections and disorganised wiring.. Its really easy to do once you have planned what you want to get to so if you are even a little DIY capable you can sort it out yourself..

 

[greeny]

Connections are poor as said by others. As for the report I would suggest a second opinion by a person who understands batteries. Your average electrician probably doesn't. (no offence intended here).
Boat surveyors do not always get it right either. I had a boat sale almost fall through because the exhaust was dripping water in the lazarrette. Leaking badly were the words used. What he didn't notice was that I had washed the boat that morning and when he lifted the lazarette hatch the water dripped inside and ran under the exhaust. He didn't check the "leak" with the engine running. Surveyors come in all levels of competence.

 

[Heckler]

Connections are poor as said by others. As for the report I would suggest a second opinion by a person who understands batteries. Your average electrician probably doesn't. (no offence intended here).
Boat surveyors do not always get it right either. I had a boat sale almost fall through because the exhaust was dripping water in the lazarrette. Leaking badly were the words used. What he didn't notice was that I had washed the boat that morning and when he lifted the lazarette hatch the water dripped inside and ran under the exhaust. He didn't check the "leak" with the engine running. Surveyors come in all levels of competence.

Indeed, my survey said I had a 3 cylinder vp engine of the 20X0 series, it isnt, its a 4 cylinder MD22,
So to the OP, do some checking yourself,

 

[lw395]

If the two batteries in a bank are giving different readings, then they are not in perfect health. The engine battery, a bit of judgement call. It will still do the job in hand when it's a long way from new, but how far do want to push that?

It's the surveyor's role to identify faults.
If the batteries still meet your needs, then you can delay replacing them.

The crimp terminations look unnacceptable to me. If much of the wiring is like that, that would be a concern as you can run up quite a bill if you need to pay marina trades to sort it. OTOH a few quid and some DIY will sort it.

 

[PaulRainbow]

Oh such a shame to have such nice batteries to then attach such crap connections to!

It would be advantageous to instruct a qualified electrician to carry out some testing as part of any negotiation, unless of course your surveyor is such?

Very simply put (at 3.30am in the morning), the only real way to test a battery properly is to disconnect, allow to settle and apply a known load over a sustained period. Calculations can then be made and conclusions drawn as to the health of each individual battery.

I agree with Matthew and i certainly wouldn't trust that battery tester.

 

[lw395]

I agree with Matthew and i certainly wouldn't trust that battery tester.

Not familiar with the model of tester, but in general, a cranking amps tester ought to give pretty much the same reading from each of a pair in a bank. One reading nearly 3x the other is not a 'happy situation'.
It indicates things need a good coat of looking at, at least.

It sounds like a quick test with some useful indication for the buyer. Personally I'd rather that than pay a surveyor to charge the batteries overnight and perform an exhaustive range of tests.

Buying a boat though, one would expect house batteries to be consumables you take as they come, surveyors are for more structural things. But pointing out work needed on the wiring and the effect it's possibly had on the batteries is a valid negotiating point for the buyer, who will need to get work done. So the surveyor has perhaps earned his fee here.

 

[Graham376]

I have tested the house bank simply by isolating each of them in turn - to within 1% or 2% each shows 13.9v, although I guess I should have allowed them time to rest after disconnecting them from the solar panels.

If I got those results from a quick look at batteries, I wouldn't be worried but, the only sure way is to do a discharge test. You could of course take them around to the local battery shop for test, some will give an honest report

 

[PaulRainbow]

Not familiar with the model of tester,

Perhaps i am ?

 

[KompetentKrew]

Oh such a shame to have such nice batteries to then attach such crap connections to!

Indeed! A crying waste if they have indeed been damaged this way.

It would be advantageous to instruct a qualified electrician to carry out some testing as part of any negotiation, unless of course your surveyor is such?

I came over to the Netherlands in January to look at a couple of boats, and have been here ever since.

This is the second Dutch surveyor I've instructed and they seem quite good at that, sitting down with the broker &/or owner after the inspection and totting up the value of what they've found. The seller and I both just accepted the surveyor's price revaluation - the full replacement cost of the batteries, I think, and 50% of the price of a new investor charger.

If the two batteries in a bank are giving different readings, then they are not in perfect health. The engine battery, a bit of judgement call. It will still do the job in hand when it's a long way from new, but how far do want to push that?

It's the surveyor's role to identify faults.
If the batteries still meet your needs, then you can delay replacing them.

Yeah, I think we'll be fine to sail the boat back to the Solent and then I'm in more familiar waters.

Very simply put (at 3.30am in the morning), the only real way to test a battery properly is to disconnect, allow to settle and apply a known load over a sustained period. Calculations can then be made and conclusions drawn as to the health of each individual battery.

What kind of load do you suggest? They are 165AH AGMs.

I'm guessing something like a 40W lamp bulb? Or 10W?

I would test the batteries by removing them then fully charging them and let them stand to see how much they drop voltage over about a week.. Then you could take them to a car battery place where they can plug on their load tester to check what CCA they are capable of..

If I only have time to do one and not both, which of these testing methods is preferred, please?

Let them stand for a week and ask Hilsea MOT centre (family run repairs garage) to put them on their tester, or discharge them over a few days with a known load measuring the voltage?

If they are are in parallel and one is bad then you will need to replace both.. Replacing just one is never a good idea..

I know, although it never hurts to have such things stated. I've just spent quite a lot of money, more than I planned to spend on a boat, and have more expenses coming up, so even if I can get just 6 months out of this pair and even if I have to run the engine or genny more often than I'd like, it'd ease the immediate financial strain.

… pointing out work needed on the wiring and the effect it's possibly had on the batteries is a valid negotiating point for the buyer, who will need to get work done. So the surveyor has perhaps earned his fee here.

About 2x - 2.5x that, including his other other observations. :encouragement:

Thanks to everyone who's replied.

 

[lw395]

Perhaps i am ?

Perhaps you're going to tell us how readings differing by a factor of nearly three don't indicate a problem? Or at least a mismatch to the point they shouldn't be paired in a bank together?

If the OP doesn't need a lot of battery capacity, he could charge both, then isolate the worse of the pair and see how life goes just using the better one? Or even take on ashore and give it a maintenance charge now and then. We did similar once, it just worked out that we took a bag of ice from Tesco for a weekend away, instead of using the fridge. Put off buying new batteries for a year, which was good, we then had new ones for a longer cruise the next year.

 

[PaulRainbow]

Perhaps you're going to tell us how readings differing by a factor of nearly three don't indicate a problem? Or at least a mismatch to the point they shouldn't be paired in a bank together?.

I didn't comment on any readings, i said i would not trust the battery tester.

 

[lw395]

I didn't comment on any readings, i said i would not trust the battery tester.

I don't disagree, just emphasising things from a different POV.
Without other tests or checks, these things are really indicators. Any battery will give a crap cranking amp reading if it's not properly charged. The big picture is that the two batteries seem to give seriously different indications and that tells us the installation needs investigation.
To actually test CCA as per any standards, you need to put the battery in a fridge at -18 or something, which is all good fun in the lab, but not much help to the ordinary boat owner.

 

[Malish]

Might be implied in earlier posts but remake the crimps with a proper crimper too

 

[sailinglegend420]

I didn't comment on any readings, i said i would not trust the battery tester.

Instead of just posting opinions why don't you post your reasons and then your posts would have more credibility and just might stop people criticising you.

If you know the tester then you should know that is for testing car batteries - it says that very clearly in the adverts and instructions.

All 'load' testers are not designed for testing proper deep cycle house batteries. The interesting things is they will normally 'pass' a bad house battery like this AGM because it can deliver enough current to start and engine, but it hasn't enough capacity left to sit at anchor and deliver small loads for a long period. But 'failing' one will always mean it is bad.

Don't bother to take them to a garage for testing, it's is so much easier to test a house battery by putting on a small load - this should be the design load for the battery in this case the Ah capacity of 165 divided by 20 (the 20 hour rating). This gives 8.25 amps.

20 hrs X 8.25 amps gives 165AH - that is how the capacity of a battery is rated for a house battery - the C/20 discharge rate. Starter batteries may be rated at C/10 or C/5 discharge current.

The OP could do a 1 hour test on the bad battery at 8.25 amps and it should last 20 hours before falling down to 10.5v. If it's bad it might go to 12.2v very quickly.

 

[PaulRainbow]

Instead of just posting opinions why don't you post your reasons and then your posts would have more credibility and just might stop people criticising you.

It's an internet forum, people post opinions. I won't post my opinion of you, because no doubt the mods would delete it.

If you know the tester then you should know that is for testing car batteries - it says that very clearly in the adverts and instructions.

Having spent the past 40 + years in the automotive and marine industry, i'm well aware of what it is. I'm also aware of the differences in batteries, something you've still not grasped.

 

[sailinglegend420]

...Having spent the past 40 + years in the automotive and marine industry, i'm well aware of what it is. I'm also aware of the differences in batteries, something you've still not grasped.

Ok that's great, so you have found anything wrong with technical details of my posts as to why 'load testers' should not have been used on those house AGMs?

 

[lw395]

Ok that's great, so you have found anything wrong with technical details of my posts as to why 'load testers' should not have been used on those house AGMs?

A load tester is a quick way of getting an indication of the state of a battery. Particularly useful when you want to check two that are paired in a bank. It doesn't matter so much what the readings are, if they are different, there is a problem.
So, problem found in a few minutes.

I'm a great believer in testing things in a way relevant to what you want from them in service, so testing a house battery by charging it fully then charting the discharge vs voltage is a superior test, but kind of pointless to pay a surveyor to do that, if his hourly rate is anything like mine it would be cheaper to just buy the new batteries.

And after all, on most boats, the house batteries are also the emergency start batteries, so it's nice to know they've got a bit of CCA.

 

[sailinglegend420]

A load tester is a quick way of getting an indication of the state of a battery. Particularly useful when you want to check two that are paired in a bank....

That's a useful and fair assessment of my postings.

The problem is when they are used by inexperienced owners.

Yes great that they tell you immediately that one is good and one is bad, but an owner should "know his boat" and realise that the bank might be faulty. That's why they should be able to come here and get these kind of tips.

The main problem with them is that inexperienced owners will be very happy when the tests tells them their house batteries are good even when they have lost a lot of capacity and are no longer useful as a house battery.

Many times in the Med I've seen owners who have had 'load' tests done on their house bank and off they go sailing to come back the next day and ask why are their batteries flat.

A short low-load test with the right discharge current for their bank showed the voltage fall to 12v in about half an hour!!!!