Correct way to check for a duff battery in a bank

[stuhaynes]

With our 24v electrics we are using 2 batteries for starting and 4 for the (modest) leisure bank. All 6 are just over 2 years old, but I think one, or maybe more in the leisure bank may be duff.

As liveaboards we can't be disconnected from 24v for too long, but I do need to check the leisure bank to see what the score is.

If I was to leave the bank on charge overnight on a high charge and then disconnect all the 4 leisure batteries from each other would I be able to leave them alone for, say, 4 hours and then check the individual voltages. Would this be enough? If so, what voltage variation would suggest a knacked battery.

Alternatively. If I was to charge the batteries as above, and then disconnect the mains and turn the inverter on, I could apply (say for instance) a 40amp load until the inverter howls, disconnect the 4 batteries from each other and then check individual voltages? (The 40amp load would come from turning on the 230V x 1KW immersion heater)

Or is there a better way that I would be able to do myself?

The batteries are each 12v 110AH wired in series and parallel to provide 220AH.

Appreciate the panel's thought. TIA

 

[Billjratt]

Since you're living aboard, I would split the domestic bank into it's two halves, then use one while investigating the other in the way you propose. Charge then monitor etc.
If you have a hydrometer just check all the cells and discard the battery which falls out of line - this can be done without disconnecting anything.
No hydrometer? shame on you! but you may get a hint if any one (or few) cells are drinking more water than the rest.
I assume the batteries don't have the tell tale that changes colour - no doubt the replacement will.

 

[jac]

To give yourself more time

Can you not temporarily split your domestic bank in 1/2 and the rely on 1 half to keep your services on whilst you test the other. If your services fail really quickly and tests on the 1/2 that you're testing reveal nothing then you've identified 2 good batteries. Then switch to the good batteries and test the other pair independently.

 

[stuhaynes]

Since you're living aboard, I would split the domestic bank into it's two halves, then use one while investigating the other in the way you propose. Charge then monitor etc.
If you have a hydrometer just check all the cells and discard the battery which falls out of line - this can be done without disconnecting anything.
No hydrometer? shame on you! but you may get a hint if any one (or few) cells are drinking more water than the rest.
I assume the batteries don't have the tell tale that changes colour - no doubt the replacement will.

Can you not temporarily split your domestic bank in 1/2 and the rely on 1 half to keep your services on whilst you test the other. If your services fail really quickly and tests on the 1/2 that you're testing reveal nothing then you've identified 2 good batteries. Then switch to the good batteries and test the other pair independently.

Thanks for both of these replies. I'm not a sparky and must admit I'd not considered either splitting the bank or using a hydrometer. I'm pretty sure I could borrow one. What range of reading would suggest a problem and what reading would suggest a good battery as opposed to the other sort?

I'm hoping to identify no more than 2 duffers, because I can use the 2 starter ones that I know are okay. I'd do this because 1/ I won't need the starter batteries 'til spring and 2/ Although my engine is industrial it is still only 2250cc, so I don't need twin 110AH batteries either

Thanks again

 

[Paddingtonbear]

Perhaps it would be helpful for you to read the Smartgauge/Merlin Electrics website, even a dimbo like what I am found it useful and no I am not inany way connected! not even a happy consumer.

 

[Kurrawong_Kid]

If your batteries are of the "no maintenance type", I dont think you can use a hydrometer because you cant access each cell. If that is so you may need to buy or borrow or hire a load tester.

 

[William_H]

Batteries

You need to separate the 2 halves of the house battery. As said use just one half after charging. Then use the other half. It will become obvious that one half is no good. (unless they are both knackered.
When on discharge if you find that one 12v battery in the series is a lot lower voltage than the other then you have identified the actual dead battery.
This test for the house batteries will test in exactly the same way as you use them. ie time to discharge at a known current.ie the inverter and imersion heater. So this is a direct indication of their usefulness to do the job. Do not expect to get anything more than 50% of the rated amp hours out of any battery and that is when it is good. good luck olewill

 

[fisherman]

I was told that no matter what the charge situation if one cell shows up a substantially different hydrometer reading from the rest it's knacked.

 

[Allan]

I have a start battery and two 110Ah domestics. At present the domestics are permanently connected together to allow them to be charged from my Rutland when I'm not at the boat.
This weekend I plan to check them by disconnecting one of them and turning on the navigation lights for an hour. I will use a meter and my BM1 to monitor the reaction. I will then swap them over and check the other one. I'm sure this is close enough to show any problem.
Allan