Another battery question...

[bluedragon]

I've followed the recent charging / battery posts with great interest and they've helped me better understand a few issues. My question also relates to one dodgy cell, but how bad is it?? The engine battery has one cell which a) has lost some electrolyte - plates just exposed b) has an SG about 0.03 lower than all the others after charging. It works OK, but I wonder for how long? It would seem from other posts that one cell is defective, taking more than its fair share of charge and losing water, and not fully charging...but it's hard to know if the problem is bad enough to change it for a new battery at this point?

The battery is 2 years old and is a calcium type low maintenance car engine start battery (I know now, not the best choice for boat use possibly). The service battery is a conventional open lead-acid 85Ah unit and is fine. I've just fitted a Sterling regulator, so this start battery is going to see 14.8V now rather than a max. of about 14.0 before.

 

[ms1]

Personally I would replace it without hesitation. when it lets you dont it will probably do so very sudenly and totally.

 

[Searush]

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Personally I would replace it without hesitation. when it lets you dont it will probably do so very sudenly and totally.

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Fairy nuff if it is your only or starting battery. I run a pair & tend to allow one to get a little "elderly" but only use it for social lighting/ entertainment etc. When the other shows the slightest sign (as above) the old one is retired & the new one become the primary battery. Thus allowing me to squeeze a bit more out of the previous primary battery for non-essential use.

 

[Chris_Robb]

Some questions:

1. Do you have a digital Multimeter? - you cannot get anywhere in diagnosing problems really with out one.

2. What resting voltages are recorded - several hours after charging? If you think its fully charged, and you get much less that 12.8V, you have a problem - by 12.4V (after heavy charging) I would chuck it out.

3. Now you have added a Stirling Charger - you will be charging your low maintenance battery at 14.8V If it is a sealed battery, you will bugger it. Read Charles Stirlings battery words - they have no place on a boat!

If you were only getting 14V before, the lighlyhood is that both your batteries will be rather sulphated, as 14V will only charge to about 75% I think. so that leaves you with a usable 25% of amps - which means you will probably have discharged the battery below 50% quite a lot, if you are not on marina mains.

All will become much clearer with a decent Multimeter! Anyway you have done the right thing by adding an alternator regulator, may be you should spend a bit more and start with a known good set of batteries.

 

[Guest]

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Personally I would replace it without hesitation. when it lets you dont it will probably do so very sudenly and totally.

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Fairy nuff if it is your only or starting battery. I run a pair & tend to allow one to get a little "elderly" but only use it for social lighting/ entertainment etc. When the other shows the slightest sign (as above) the old one is retired & the new one become the primary battery. Thus allowing me to squeeze a bit more out of the previous primary battery for non-essential use.

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Man after my own heart !!

 

[bluedragon]

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Some questions:

1. Do you have a digital Multimeter? - you cannot get anywhere in diagnosing problems really with out one. ANSWER = YES

2. What resting voltages are recorded - several hours after charging? If you think its fully charged, and you get much less that 12.8V, you have a problem - by 12.4V (after heavy charging) I would chuck it out. ANSWER = 12.8V

3. Now you have added a Stirling Charger - you will be charging your low maintenance battery at 14.8V If it is a sealed battery, you will bugger it. Read Charles Stirlings battery words - they have no place on a boat! ANSWER = NOT SEALED. I'VE READ THAT Ca MODIFIED BATTERIES NEED 12.8V.

If you were only getting 14V before, the lighlyhood is that both your batteries will be rather sulphated, as 14V will only charge to about 75% I think. so that leaves you with a usable 25% of amps - which means you will probably have discharged the battery below 50% quite a lot, if you are not on marina mains. ANSWER = LOOKED AFTER THEM QUITE WELL, WITH MAINS CHARGING WHEN POSSIBLE. SERVICE BATTERY HAS AT LEAST 70% CAPACITY FROM TESTS I'VE JUST DONE.



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I'd normally assume this battery is OK...it's just that one cell that conerns me.

 

[ccscott49]

One cell is the battery, if one cell is duff the baqttery is duff, if it's your start battery, replace it, otherwise you may end up another RNLI statistic. IMHO

But first get it tested by a proffesional battery service/supply place.

But from what you say, I think it's cream, crackered!

 

[VicS]

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I'd normally assume this battery is OK...it's just that one cell that conerns me

[/ QUOTE ] A SG differece of 0.03 is not a huge diffrence but I think you would be right to keep an eye on it. Personally I am a fan of the multimeter approach. It should be possible to charge a good battery with a mains charger so that it reads around 12.70volts after resting for 12 hours. A newish one should get to 12.8 maybe a bit higher. If the battery is Ok it should still be around 12.6v if left standing for several weeks.

A long bench charge might bring the suspect cell up more in line with the others (You have not measured the SG after topping up recently have you? It takes quite a time for the top up water to mix completely with the acid. Re-reading your original post, if the plates were exposed you must have topped it up before you could use the hydrometer so give it a good charge and check it again)

If you find that cell needs frequent topping up then definitely suspect it is dodgy.

I dont think you are right in believing that one cell is taking more than its fair share of the load or the charging. All the cells are in series so they will all see the same charging current or discharge current.

If you can use your service battery for engine starting in an emergency then you have no worries should this battery suddenly fail.

Getting it tested is a sensible suggestion but you always have to bear in mind that the people you get to test it are in busines to sell batteries! At only two years old does it not still have a guarantee?

 

[bluedragon]

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Getting it tested is a sensible suggestion but you always have to bear in mind that the people you get to test it are in busines to sell batteries! At only two years old does it not still have a guarantee?

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I might well do that. It has a 4 year Halfords guarantee, but I assume only when used as a car battery. I've had batteries tested by them before and even a sulphated battery that I got rid of was "just OK" for engine starting according to them!!