Faulty battery in a battery bank

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marcot

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The 24volt battery bank (4 x6v 225ah) has one dead battery. The other three are fine . Batteries are 6 yrs old.
I will buy a new one. Any issue with the old three?
 
marcot said:
The 24volt battery bank (4 x6v 225ah) has one dead battery. The other three are fine . Batteries are 6 yrs old.
I will buy a new one. Any issue with the old three?
Click to expand...

Shouldn't be, especially if, as you say, they're fine. But, at 6 years old, they're not going to last for ever.
 
Are those T105 or similar?
That's a bit of a disappointing life unless heavily used - are they?
How has it failed - internal short, no capacity or what?
Mixing one new with 3 old that could be near end of life could be throwing good money after bad.
However you may just have been unlucky and might get a few years out of them.
Not enough info to say or even guess!
 
The danger for you is that your 3 older batteries may shorten the life of the new one. I have always understood that batteries are best changed in sets.
 
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good (conventional) practice says that if you replace a battery, it is easier for the charging system if the new one is the same type and capacity as the old ones. Then they are all treated the same by the incoming volty things, and the charger does not attempt to stop if one battery has a lower capacity than the others, or keeps on stiuffing power into three small ones if there is one which still needs charging.

6 years is getting on a bit. Might be worth finding someone with a heavy discharge battery tester, or isolating the batteries one by one and doing a discharge test with a 50w 12v car bulb, and seeing what happens to the voltage after 1hr, 6 hr, 12 hr, and how long it takes for the batteries to recover with a 'clever' recharge, and what happens to the voltage after 24 hrs.

Failure of one in a series raises reliability questions. How risk sensitive are you ? :)
 
sarabande said:
good (conventional) practice says that if you replace a battery, it is easier for the charging system if the new one is the same type and capacity as the old ones. Then they are all treated the same by the incoming volty things, and the charger does not attempt to stop if one battery has a lower capacity than the others, or keeps on stiuffing power into three small ones if there is one which still needs charging.
Click to expand...

Same chemistry, but not necessarily the same capacity. Batteries in a bank accept charge according to their individual requirements.
 
Your old batteries will in reality no longer be 225ah but more like 100ah in view of their age. So putting three 100ah batteries in series with a new 225ah is not good practice.
The internal resistance of the old batteries will undoubtedly be higher possibly limiting the charging current, and they will reach 'full' charge before the new one does so may start gassing.
In addition, if the old ones are now only 100ah, they will clearly be discharged before the new one, which is therefore never able to be used to its full extent.

Personally, I replace the dead one with a 120ah as a stop gap until could afford to change the other 3. (or a 225ah if I could change the others quite soon)
 
ianj99 said:
Your old batteries will in reality no longer be 225ah but more like 100ah in view of their age. So putting three 100ah batteries in series with a new 225ah is not good practice.
The internal resistance of the old batteries will undoubtedly be higher possibly limiting the charging current, and they will reach 'full' charge before the new one does so may start gassing.
In addition, if the old ones are now only 100ah, they will clearly be discharged before the new one, which is therefore never able to be used to its full extent.
Click to expand...

Batteries in a parallel bank accept charge, and provide current, according to their individual characteristics. If you had flat and charged batteries in a battery bank, they'd be at different voltages, but they can't be because they're all connected.
 
Batteries are Trojan T105. New one will be the same
Heavily used until last year.
The dead battery started gassing when charging and became "hot".
Other batteries after 24 hrs rest from full charge are 6.5v.
 
Just keep an eye on the other 3 - they may go the same way. Voltage is a poor indicator but I would expect the old ones to drop more quickly than the new one under load.
The gassing and heating up is because all the charging current passes through all the batteries whether they need it or not.
 
marcot said:
Batteries are Trojan T105. New one will be the same
Heavily used until last year.
The dead battery started gassing when charging and became "hot".
Other batteries after 24 hrs rest from full charge are 6.5v.
Click to expand...

Gassing just in one cell or all three?
What voltage does it show after trying to charge?

It seems unlikely that your others are "fine" if you do a test discharge you'll probably find capacity is way down as someone said. Ideally check at about 10A for this size battery. High rate tests don't tell you much about low rate capacity.
In industrial situations you normally change if capacity is below 80%. If you are much below that they are near end of life and reliability impaired. Not unreasonable after 6 years heavy use.
If that's the case you really need to replace all.
 
Before making any decision I'd suggest doing a full discharge/recharge on the whole bank then do an individual charge/discharge on each battery - you may find the duff battery recovers sufficiently to continue being used - at least you'll know how far off life termination they all are.
I'd be very loath to mix one new battery in a series of 4.
 
If it were me as said I would look carefully at the remaining 3 batteries. Do an individual discharge test with a load of about 10 amps. See which one has worst capacity and replace that as well. Put the 2 new batteries in series then in parallel with the 2 older. Obviously you have already found you need to isolate each series pair from the other parallel pair. keep a close watch on the older series pair as eventually they will also die. You might in fact do better to fit isolation switches to each parallel pair so you can use them separately.
Certainly if you do just replace the one battery you need to monitor the function of each set of series batteries as if one battery dies it could pull down all batteries so risking the new one. good luck olewill
 
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