house battery bank

[spencers]

One of my 2 house battery banks has failed and I need to replace the batteries in that bank.
Is it ok to replace just one bank (4x6v deep cycle) of the same brand and size as the the other bank that are now 30 months old and in good condition?

 

[SteveK]

I will say yes if the two house banks are actually separate and are charged separately and not as one large bank.
But why have two separate banks of 4x6V batteries instead of one bank of 8. Just curious, not suggesting you make one group.

 

[Shrew]

One of my 2 house battery banks has failed and I need to replace the batteries in that bank.
Is it ok to replace just one bank (4x6v deep cycle) of the same brand and size as the the other bank that are now 30 months old and in good condition?

You have Two (4x6V) battery banks? Why?? In fact, this would seem like a horrible use of batteries. The idea is to draw down as little as possible. Here you draw down half the bank twice as much.

In the long run, you would get longer life out of an 8 x 6V bank you're drawing into half as much.

 

[Bacchus]

You have Two (4x6V) battery banks? Why?? In fact, this would seem like a horrible use of batteries. The idea is to draw down as little as possible. Here you draw down half the bank twice as much.



In the long run, you would get longer life out of an 8 x 6V bank you're drawing into half as much.

Shrew
On the surface that sounds reasonable but stop and think about it a little bit more.
Scenario #1 - If combined and you draw down half as much... say each day... then you recharge. Equals one cycle / day on all battys.
Scenario #2 - If manage as 2 separate banks you draw bank A down twice as much and recharge it day 1. Day 2 you do the same with bank B and recharge. You had half as many cycles on each bank as you alternate days.
So yes you get fewer cycles in the life of a batty drawing it down farther but you also use it half as often... its a wash other than a very small difference.
Basically battys provide a fixed # of AHs over their life, unless you kill them prematurely. How you use it is up to you. Many will say a batty is some how "Damaged" if drawn down more than 50% DOD but IMO that's a myth that manuf & their batty lIfe cycle charts do not support. Happy to provide a more complete analysis I did to convince myself if you'd like.

 

[friz]

As Soo Valley said and again if the banks are electrically isolated from each other, yes.

 

[koliver]

One of my 2 house battery banks has failed and I need to replace the batteries in that bank.
Is it ok to replace just one bank (4x6v deep cycle) of the same brand and size as the the other bank that are now 30 months old and in good condition?

2 house banks? Two load centres? AC fridge? AC galley?
Since we don't have any information that will explain the reason for the extra battery bank, I will supply a scenario: When new, the boat came with one bank. The owner became aware that his AC consumption, through inverters, was not being met on that one bank, so added another, in a convenient location that was not close enough to the original bank to become part of it. Now there are two banks, of different ages. The older one or the one getting the higher useage has now failed, so must be replaced. There is still no way to add new batteries onto the other bank, due to location and space issues.
Back to the question.
Do what you have to do. Your existing bank is being charged and discharged separately from the failed bank, so really doesn't care what you do there. All together would be a better system, KISS principle applies, but nothing you are asking for will be "wrong".

 

[backinblue]

Shrew
On the surface that sounds reasonable but stop and think about it a little bit more.
Scenario #1 - If combined and you draw down half as much... say each day... then you recharge. Equals one cycle / day on all battys.
Scenario #2 - If manage as 2 separate banks you draw bank A down twice as much and recharge it day 1. Day 2 you do the same with bank B and recharge. You had half as many cycles on each bank as you alternate days.
So yes you get fewer cycles in the life of a batty drawing it down farther but you also use it half as often... its a wash other than a very small difference.
Basically battys provide a fixed # of AHs over their life, unless you kill them prematurely. How you use it is up to you. Many will say a batty is some how "Damaged" if drawn down more than 50% DOD but IMO that's a myth that manuf & their batty lIfe cycle charts do not support. Happy to provide a more complete analysis I did to convince myself if you'd like.

Hi Bacchus,

I understand what you are trying to say here but if I could poke a hole in your logic it would be that instead of alternating banks and recharging daily, if they were combined you would have twice the capacity and could recharge every other day and still have the same number of charge cycles as your alternating example, no? Or the other option is to recahrge daily but the banks would be at 75% instead of 50%. In theory I think that may extend the battery life too. Unless there is a good reason to have 2 banks, personally I think I'd prefer 1 larger one just to know that I have more than enough for a particular time period like a night at anchor.

 

[Shrew]

I suppose if you look at deeper discharge over less cycles could come close to being a wash as compared to shallower discharges over more cycles. But the other side is, if you have 2 banks of 4 x 6vdc batteries and one battery dies, you need to remove the other battery to maintain 12V. This means that one of your banks is half the size of the other.

if you have a single 8 x 6v bank, one batt. dies, you remove the other and have a 6 x 6v bank.

 

[SteveK]

I suppose if you look at deeper discharge over less cycles could come close to being a wash as compared to shallower discharges over more cycles. But the other side is, if you have 2 banks of 4 x 6vdc batteries and one battery dies, you need to remove the other battery to maintain 12V. This means that one of your banks is half the size of the other.

if you have a single 8 x 6v bank, one batt. dies, you remove the other and have a 6 x 6v bank.

I along with some others seem to think that a lesser discharge before recharge on FLA will make them last longer. unproven perhaps.
different battery types have different discharge charge needs.
I have 6x6V bank which is what I need. I never considered a 2 bat bank and a 4 bank bat system it discharging to the max on one or other on a regular basis.

 

[Bacchus]

Hi Bacchus,

I understand what you are trying to say here but if I could poke a hole in your logic it would be that instead of alternating banks and recharging daily, if they were combined you would have twice the capacity and could recharge every other day and still have the same number of charge cycles as your alternating example, no?
Or the other option is to recahrge daily but the banks would be at 75% instead of 50%. In theory I think that may extend the battery life too. Unless there is a good reason to have 2 banks, personally I think I'd prefer 1 larger one just to know that I have more than enough for a particular time period like a night at anchor.

Backinblue...
Yes absolutely agree with the first part and that was my point you reinforced.
By combining you could run twice as long before recharge but then the DOD or SOC would be the same as if you ran a separate bank half as long and switched to the other bank.
I'm certainly NOT trying to imply that separate is some how better than one large, only that the all too common fallacy that DOD beyond 50% is somehow harming a battery and they last "longer" by not exceeding that magic number. In that case longer is really more cycles and if you strive for lower DOD you use up those "extra" cycles recharging more frequently.
There is a small gain in total AH over the batty life but it is rather small... around or less than 10% not the 50% gain often stated when people confuse cycles with years of life.

 

[backinblue]

Slightly off-topic but maybe of some interest. The LiPo battery for my small electric outboard is not real clear on how to store it when not in use. They do say that ideally you should store it at 60% but I have no idea how to determine the current state of charge w/o connecting it to the motor. I have since learned it is not good to keep it connected to the charger for long periods of time once it's charged. Once it is disconnected, it will self-discharge at a slow rate. What I am currently doing is charge it at the end of season then disconnect it and reconnect every month or 2 to re-charge. Anyone else dealing with this?