Battery drop testers

Pavalijo

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At the end of the 2017 season I turned everything off and left a 30w solar panel connected to the batteries via MPPT regulator, left the boat in France and went home.
I returned in January for a mid winter check to discover that I had left the inverter switched on ( no load but it draws current still) and the batteries not registering on the voltmeter (which shows from around 11v) - the panel lights were very dim and I thought I had completely ruined my one year old bank of Rolls AGMs.
I plugged into the power and turned the Victron charger on.

Next day I returned to the boat with a battery drop tester loaned by my pal who we were staying with nearby. It looked exactly like this one, from memory.

I performed the test expecting the worst. However the tester suggested that the batteries were fine.

As we launched in April we still expected the worst, but living aboard for 5 months and traveling from Brittany to Galicia, spending 26 nights at anchor, I have to say that the batteries performed as though the deep discharge had never happened.

At the end of last season we discovered that there would have been something else drawing current (still have to work out what it was), so we just disconnected the batteries.

So I would say that the drop charger was worthwhile and that the Rolls AGM recovered well from my abuse!)
 

lw395

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Is this sort of tester any good in determining whether a battery needs replacement?
https://www.ebay.co.uk/itm/6V-12V-1...m=113586818702&_trksid=p2047675.c100005.m1851
It has its uses.
Knowing if your battery will put out 100A or whatever is helpful in knowing a) if it's charged and b) serviceable to start an engine.
It's less use for a house battery.
I have an old battery in the shed, taken from a neighbour's car. It will deliver 200A for 20 seconds if it's charged up, but, it has very low capacity, about 10Ah(?). It also loses charge over a week or so.
So that battery would pass a test with this tester, but IMHO it wanted replacing, even as a 'start' battery.

If a battery 'failed' on a tester like that, it might just be telling you it needed better charging.
But at least that would stop you rushing out and buying a new starter motor.
Measuring something is usually a step forwards, but interpreting the results is the important thing.
 

Norman_E

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I think it may be worth the small cost. I have three house batteries , all the same make and AH rating connected in parallel and charged together. If I disconnect them after fully charging to the point where the charger drops into float mode and then switches itself off, and test each one in turn I am hoping that such a tester will identify whether there is one weaker than the others, which is what I currently suspect.
 
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William_H

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Batteries die in 2 ways. Firstly from slow deterioration of the usable capacity. The other way is sometimes suddenly sometimes slowly losing the ability to provide a large current for engine starting. The discharge meter in the link IMHO is somewhere between the 2. Too much current for checking long slow discharge for capacity. Too little current to really check ability to start an engine. You can with a bit of experience detect by ear if an engine start enthusiasm is declining and likewise when using your services over a long period develop a sense of when batteries are losing capacity.
Certainly with multiple batteries in parallel you need to disconnect all but one and check it's performance as above then check the others individually. A comparison should show up any failures. In other words throw a battery away when it won't do the job you need. Looking for potential failure in future is not very successful. ol'will
 
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