AGM batteries - how reliable is CCA testing?

[rszemeti]

The only way I have reliably found to assess batteries with equipment that any Yachtsman can easily get hold of is to stick a bunch (usually about a 4 or 6) 12v 55W car headlight bulbs onto some wire, and then separate the batteries and hang the bulbs on for a while.

4 bulbs should run for around 5 hours on a good 100 amp-hour battery ... 3 of my six batteries failed to make ti past 30 minutes.

it's a simple test to do, costs less than a £20 in parts and is an actual real rest of capacity, not some indicative figure that may or may not represent a batteries actual performance.

 

[lw395]

The only way I have reliably found to assess batteries with equipment that any Yachtsman can easily get hold of is to stick a bunch (usually about a 4 or 6) 12v 55W car headlight bulbs onto some wire, and then separate the batteries and hang the bulbs on for a while.

4 bulbs should run for around 5 hours on a good 100 amp-hour battery ... 3 of my six batteries failed to make ti past 30 minutes.

it's a simple test to do, costs less than a £20 in parts and is an actual real rest of capacity, not some indicative figure that may or may not represent a batteries actual performance.

£20 in parts, but >£200 in labour if you're paying a surveyor to do it.

 

[rszemeti]

You know the bit where it says "with equipment that any Yachtsman can easily get hold of" ... that is supposed to indicate that "this is something you can do yourself, possibly as part of your regualr winter maintenance checks.

It is not the sort of thing you would get a surveyor to do, as that's not what they do. It would be even more expensive to get a heart surgeon to do it, but it is about as relevant. Apart from that, asking a surveyor to check a boat is basically a waste of time, the things you actually care about will be covered by "we didn't inspect this, and cannot be held to account over it" and the rest of the stuff will just be random dribble about stuff they never bothered to look at in the first place.

 

[rszemeti]

I should also add that CCA testing of leisure batteries is mostly pointless, I would expect even new/fresh/fully charged ones to show a fail on a CCA tester. Leisure batteries are built to maximise the storage medium and minimise the support structures and conduction structures.

If you want peak amp output, buy a combination use battery, if you want maximum storage capacity for a given volume, buy a leisure battery, but do not expect to get many peak amps out of it, it is not what they do.

 

[PaulRainbow]

I should also add that CCA testing of leisure batteries is mostly pointless, I would expect even new/fresh/fully charged ones to show a fail on a CCA tester. Leisure batteries are built to maximise the storage medium and minimise the support structures and conduction structures.

If you want peak amp output, buy a combination use battery, if you want maximum storage capacity for a given volume, buy a leisure battery, but do not expect to get many peak amps out of it, it is not what they do.

What is a "combination battery" ?

What is a "leisure battery" ?

 

[lw395]

You know the bit where it says "with equipment that any Yachtsman can easily get hold of" ... that is supposed to indicate that "this is something you can do yourself, possibly as part of your regualr winter maintenance checks.

It is not the sort of thing you would get a surveyor to do, ......

If you read the OP, the surveyor has done a CCA check and used it to highlight some issues.

 

[MikeCC]

Blimey, this is hard work. The surveyor has identified a potential problem with batteries. Like anything, you don't expect the surveyor to do any more. He doesn't take apart the rigging and test each wire

As Matthew suggested early on, you take them to someone with a constant current load tester and errr... get them tested. Just make sure they recharge straight after CCA/automotive drop tests, waste of time. If it still has functioning capacity, it will start the engine. Job done.

 

[rszemeti]

If you read the OP, the surveyor has done a CCA check and used it to highlight some issues.

Has he? or has he simply mis-used a CCA tester and spotted an "issue" where one possibly does not exist?

Batteries come in various flavours ... and with different purposes. You want your "engine start" batter to deliver a lot of cold crankign current .. as such, it has thick plates. It is optimised for the number of amps it can provide into the starter, under extreme conditions.

The "house" batteries may be of a type optimised for energy storage density, they may store 50% more charge than the "engine start" battery ... but have much lower CCA

Have a look at this "deep cycle" AGM battery .. 115AH, 550 CCA ...

https://www.varta-automotive.com/en-gb/products/varta-professional-deep-cycle-agm/830-115-060

and this "Engine Start" AGM battery, 105AH, but 950 CCA

https://www.varta-automotive.com/en-gb/products/varta-silver-dynamic-agm/605-901-095

Two similar technology batteries, of roughly the same capacity .. but one has nearly twice the CCA of the other ... if you had used a CCA tester on these, you might have (wrongly) concluded one was faulty when you got a very different reading.

CCA testers have limitations, not everyone understands them.

 

[PaulRainbow]

Batteries come in various flavours ... and with different purposes. You want your "engine start" batter to deliver a lot of cold crankign current .. as such, it has thick plates.

Nope, starter batteries have thin plates.

 

[sailinglegend420]

....you take them to someone with a constant current load tester and errr.....If it still has functioning capacity, it will start the engine. Job done.

The surveyor was testing AGM deep cycle batteries - drop testers are only designed to test starter batteries. The battery with a high CCA passed the test so may start the engine, but may still be useless delivering low currents for a long time as a house battery.

Education, education, education.....

Tell people what you are going to tell them, then tell them, then tell them what you've told them.

 

[lw395]

The surveyor was testing AGM deep cycle batteries - drop testers are only designed to test starter batteries. The battery with a high CCA passed the test so may start the engine, but may still be useless delivering low currents for a long time as a house battery.

Education, education, education.....

Tell people what you are going to tell them, then tell them, then tell them what you've told them.

Read the OP.
The point of the test was for the surveyor to quickly show that the installation was not optimum and had resulted in an imbalance between the batteries of the bank.
Job Done.

Victron AGM batteries are specified to have a CCA performance, looks like it should be 600A at 0degF?
So testing it and getting less than 300A indicated is a strong suggestion that it's not what it should be.

 

[sailinglegend420]

Read the OP.
The point of the test was for the surveyor to quickly show that the installation was not optimum and had resulted in an imbalance between the batteries of the bank.
Job Done....

Agree 100% with that, but all I'm trying to explain - again - is that drop testers can give a false positive. I've you are a surveyor then yes a useful tool - for the rest of us not useful if it gives an inaccurate result when testing deep cycle batteries.

Now I told everyone what I told them - again.......again.

By the way the Victron AGM does not have the CCA printed on it so how can the surveyor input the correct CCA rating before the test. I doubt he goes online to check that, so any value will do. And as you pointed out an imbalance of 3-1 in the CCA values between the batteries shows a problem so he was absolutely correct in his report.

 

[pvb]

The point of the test was for the surveyor to quickly show that the installation was not optimum and had resulted in an imbalance between the batteries of the bank.

I'm not sure that was the point at all. I reckon the surveyor was just using his fancy fifty-quid battery tester as a routine check; an easy way to add a bit to his report. I wouldn't necessarily place much reliance on the readings, as others have said there are better ways of checking batteries.

However, as you said in post 8, when you buy a boat you can usually expect to have to replace some consumables like batteries.