Tired Old meets Fresh New Battery

[sailinglegend]

Originally Posted by Wissing

Nice to see somebody who knows his stuff.

It's a shame you have been so taken in by ALL of Andina's comments! I've been waiting for others to correct Andina on some errors in her posting but nobody has - so I offer my understanding of the situation.

Originally Posted by Andina Marie

Although the answers you've received are very common and pervasive in bulletin boards they are wrong. Their advise would be correct for batteries in SERIES but it does not apply to batteries in PARALLEL.

Each battery will contribute to the whole capacity in proportion to its own capacity. The OLD one can't "run the new ones down".

Yes you are correct in saying that you can connect batteries of different capacities in parallel - this used to be thought as a no-no - but everyone else in the industry suggests you are wrong in saying that you could can mix any age or type. Both Mastervolt and Lifeline say you can mix capacities, but they add that they must be of the same age and type.

Sabre yachts, which use Lifeline AGMs, regularly ship with different sized batteries to be able to get the maximum capacity from all the available space. Lifeline Batteries were so concerned about this that they carried out extensive research that proved that a bank can be made up of different capacities and that the life of the batteries was not compromised, as long as they are all the same type and the same age.

If is impossible to find other examples on the net as to why they must be the same type and age, but, as an electrical engineer, I believe it is all to do with open circuit voltage.

Originally Posted by Andina Marie

For one battery to run another one down it would have to be at a different voltage. While it is true that when you first connect there will be voltage differences and current will flow for a few seconds but then they will then all be at the SAME voltage. If at the same voltage no current flows between the batteries.

Yes the batteries are at the same voltage when connected in parallel - but what voltage? For a given state of charge different types of batteries have a different voltage and as batteries age that voltage changes. So 12.2 volts may be the voltage at 50% SoC, but an old battery may be only 12.1 volts. Similarly a 100% SoC may be 12.8 for a new battery, but only 12.65 for a different type or age.

So what happens when a new battery at 12.8v open circuit is connected in parallel to an old battery of 12.65v, i.e. no load. Yes the voltage of the combined bank stabilizes quickly at maybe 12.7v or less, certainly not 12.8volts, so already the “bank” has lost some useful volts. That voltage has gone in raising the voltage of the old battery so the new battery is being pulled down by the old battery. There is only about 0.6v between being fully charged and empty at 12.2v so a loss of only 0.1 volt in the bank voltage is significant.

The effect of this “dragging down” the new battery will get worse as the old battery gets older – you may never see the effect unless you regularly disconnect the batteries and do extensive tests and charts. This will undoubtedly shorten the life of the new battery – and we need to do everything we can to try and lengthen the life of our batteries not put another nail in their coffin by mixing old and new.

Originally Posted by Andina Marie

When connecting in parallel you can mix different size, different age, even different chemistry except that you may have to set your charger to suit the most critical battery, for example a lead-acid in parallel with a sealed gel battery should be charged at the gel battery rate, not the lead acid rate, so charging may take a few minutes longer but they will still all get a full charge.

This is probably the worst piece of advice in this posting. Yes they may eventually get a full charge but they higher voltage battery will sulphate in the process, shortening its life considerably. Batteries need to reach their “Gassing” voltage in order to help reduce sulphation and stratification – the electrolyte needs to bubble to mix it up properly. Combining a gel battery, which wants 14.1v maximum, with a flooded lead acid that needs 14.8 volts is very bad advice.

You have to realise that Andina’s posts are always to promote and justify the effectiveness of her battery combiners. I challenge her, or anyone, to come up with ANY independent scientific research to support her claims that mixing batteries of different types and age in a single bank is totally acceptable.

[elhix]

Ah! Internet forums... Where definitive information thrives.

[carstenb]

I'm not a EE. Some years ago I installed an autopilot on my old boat and added a battery since autopilots use a fair amount of Electricity. Took about 4 months but one day the boats was filled with very nasty fumes and I had to disconnect the old battery in a hell of hurry.

Lesson learned? Never mix batteries

[Pete7]

So we have a "tired old battery" that has been down to 11v once already by being left unattended, how much longer is this old battery going to go on for? The yacht is a 32ft cat so is weight important? a 150 AH battery isn't exactly light.

I would take the old battery down to the scrap yard and weigh it in, then stick the two new ones in. Looked after with some solar panels you probably won't have another problem for 6 or 7 years.


Pete

[MarkJ]

The 'old' battery is only 2 years old and been down once.

I would stress test it against the new and then put it in with the new.

Mark

[Andina Marie]

Originally Posted by sailinglegend

It's a shame you have been so taken in by ALL of Andina's comments! I've been waiting for others to correct Andina on some errors in her posting but nobody has - so I offer my understanding of the situation.



Yes you are correct in saying that you can connect batteries of different capacities in parallel - this used to be thought as a no-no - but everyone else in the industry suggests you are wrong in saying that you could can mix any age or type. Both Mastervolt and Lifeline say you can mix capacities, but they add that they must be of the same age and type.

Sabre yachts, which use Lifeline AGMs, regularly ship with different sized batteries to be able to get the maximum capacity from all the available space. Lifeline Batteries were so concerned about this that they carried out extensive research that proved that a bank can be made up of different capacities and that the life of the batteries was not compromised, as long as they are all the same type and the same age.

If is impossible to find other examples on the net as to why they must be the same type and age, but, as an electrical engineer, I believe it is all to do with open circuit voltage.

How would open circuit voltage be a factor, they are connected together, they are not open circuit, they are at the SAME voltage. As an electrical engineer you "believe" it is to do with open circuit voltage but have no idea why.

Yes the batteries are at the same voltage when connected in parallel - but what voltage? For a given state of charge different types of batteries have a different voltage and as batteries age that voltage changes. So 12.2 volts may be the voltage at 50% SoC, but an old battery may be only 12.1 volts. Similarly a 100% SoC may be 12.8 for a new battery, but only 12.65 for a different type or age.

So what happens when a new battery at 12.8v open circuit is connected in parallel to an old battery of 12.65v, i.e. no load. Yes the voltage of the combined bank stabilizes quickly at maybe 12.7v or less, certainly not 12.8volts, so already the “bank” has lost some useful volts. That voltage has gone in raising the voltage of the old battery so the new battery is being pulled down by the old battery. There is only about 0.6v between being fully charged and empty at 12.2v so a loss of only 0.1 volt in the bank voltage is significant..

OF course the voltage of the higher one will be lower DUH! and the voltage of the lower one will be higher. You moved energy from one battery to the other but lost very little in the process.

But we are talking about an installation where this happens once when they are installed and from then on act as a single battery. Even if the voltage was 0.1 volts less during installation that has no bearing on subsequent use, voltage will be restored on the first charge and from then on they remain the same.

The effect of this “dragging down” the new battery will get worse as the old battery gets older – you may never see the effect unless you regularly disconnect the batteries and do extensive tests and charts. This will undoubtedly shorten the life of the new battery – and we need to do everything we can to try and lengthen the life of our batteries not put another nail in their coffin by mixing old and new.

You refer to this dragging down but don't explain how this can happen. The self discharge rate of an older battery may be somewhat more than a new battery so if the discharge rate of the old one is twice that of the new one, then there will be current flow from battery to battery. But it is insignificant. If the discharge rate of the old battery 2% per month instead of 1%, that is 2amp-hours per month which calculates to 3 thousandths of an amp of dragging down instead of 1.5 thousandths of an amp.

This is probably the worst piece of advice in this posting. Yes they may eventually get a full charge but they higher voltage battery will sulphate in the process, shortening its life considerably. Batteries need to reach their “Gassing” voltage in order to help reduce sulphation and stratification – the electrolyte needs to bubble to mix it up properly. Combining a gel battery, which wants 14.1v maximum, with a flooded lead acid that needs 14.8 volts is very bad advice.
.

There is some truth in this in the case of mixing lead-acid and sealed batteries. Once or twice a year you can remove the sealed battery and switch to lead-acid equalizing settings but to be honest, with over 50 years experience on charging and using batteries I've not seen any suddenly sulfate up because you limited maximum voltage to 14.2.

You have to realise that Andina’s posts are always to promote and justify the effectiveness of her battery combiners. I challenge her, or anyone, to come up with ANY independent scientific research to support her claims that mixing batteries of different types and age in a single bank is totally acceptable.

HUH??
WHERE IN THIS THREAD DID I MENTION BATTERY COMBINERS (apart from this line )?
I encounter resistance in these forums because I am a manufacturer and some resent the free advertising. But it so happens that I have over 50 years experience in these subjects so that is where I comment. You should be grateful that there is a manufacturer helping sort out the information here. You quote battery manufacturers with differing opinions. Where are THEY posting here? Do they not have a vested interest in selling their batteries?

[sailorboy1]

I accept that an old old battery in parallel with a new battery increases total capacity. I don't really understand how anyone can really say otherwise. It isn't any different than paralleling batteries of different size.

The only question is whether the old battery in effect results in a shorter life for the new battery. But it always has seemed like splitting hairs as house batteries live kind of a rough life and whether a battery lasts 6 years or 7 is as much luck during that time as anything else.

Batteries are cheap for their use and life and we spend too time wasting excess worry on them!

[sailinglegend]

Originally Posted by Andina Marie

.....You quote battery manufacturers with differing opinions. Where are THEY posting here? Do they not have a vested interest in selling their batteries?

Lifeline posted their information on this excellent site:

Mixing Battery Sizes In One Bank On A Boat

You haven't offered your sources of information - so you must be the ONLY person who believes in mixing different types and different ages?

[donradcliffe]

I've only messed around with batteries on cruising boats for over 20 years, but I have to say that Andina has it right and the urban myths about not mixing ages and types are sales promotions by the battery manufacturers.

I have had matched batteries, and have had mixed types/sizes/new/old batteries in parallel as a result of having some batteries fail and buying what is available locally. They behave exactly like Andina says, because that is the law of physics. They are all at the same voltage, and the strongest battery gives/accepts the highest current. There may be some energy transfer/loss when you initially connect the batteries, but no significant loss on an ongoing basis.

The advantages of making one large bank far outweigh using separate banks for two reasons--Peukert's law says you will get more amp-hours out of the combined bank and it will take fewer amp-hours to recharge the combined bank, and the combined bank will last longer because the number of daily discharge cycles a battery will last is a non-linear function of the depth of discharge.

I did have one cell failure (not in the oldest battery) in twenty years--it dropped the bank voltage down to where alarms went off and I had to find and disconnect the bad battery. It wasn't hard to find, as the cell was hot. There was enough energy remaining in the other batteries to start the engine and recharge them.

[MarkJ]

Originally Posted by sailorboy1

Batteries are cheap for their use and life and we spend too time wasting excess worry on them!

Hang on! Mine are $500 each and I have two! If I was going to throw $1,000 in the trash like folks are recommending the OP do then I would be a tad upset.

There are so many threads on here that say people can live on $500 per month but then you want to throw out 2 year old batteries?

There must be a better way!

Mine are nearly 3 years old and I need to add a third. So I will add a third one which will be new. So I can spend $1,500 or $500. Its doesnt take much figuring

[sartorst]

I would bet money that most peoples opinion will change through the years about batterys ,type, use ,charging ,quality, income, tolerance level, how far from home,etc, depends on the type cruising your doing?
as I set here,at home contemplating my opion on this
There was the any thing will do period
then there was the big new time
back to just batterys
then the look back at the HOW MUCH have I spent?

[sailorboy1]

Originally Posted by MarkJ

Hang on! Mine are $500 each and I have two! If I was going to throw $1,000 in the trash like folks are recommending the OP do then I would be a tad upset.

There are so many threads on here that say people can live on $500 per month but then you want to throw out 2 year old batteries?

There must be a better way!

Mine are nearly 3 years old and I need to add a third. So I will add a third one which will be new. So I can spend $1,500 or $500. Its doesnt take much figuring

I said they are cheap for their use and life. Batteries are in use 24/7 and should last at least 5 years (longer really). So in the end if you spent $1500 (I spent $500 for my 460AH bank) that is $300/yr, or $25/mo, or $0.82/hr. That is less than most people, especially Aussies, spend on beer

BTW - I didn't think you supported the $500/mo story. And please note that I never said to throw the old batteries away, I said I didn't see any reason that they couldn't be used (since you chose to quote me with a suggestion I'm part of a rich throw crap away boater crowd)

[MarkJ]

Originally Posted by sailorboy1

That is less than most people, especially Aussies, spend on beer

BTW - I didn't think you supported the $500/mo story.

Putting those two sentences together you'll understand why!

Mark

[FlyingCloud1937]

Originally Posted by Andina Marie

How would open circuit voltage be a factor, they are connected together, they are not open circuit, they are at the SAME voltage. As an electrical engineer you "believe" it is to do with open circuit voltage but have no idea why.


OF course the voltage of the higher one will be lower DUH! and the voltage of the lower one will be higher. You moved energy from one battery to the other but lost very little in the process.

But we are talking about an installation where this happens once when they are installed and from then on act as a single battery. Even if the voltage was 0.1 volts less during installation that has no bearing on subsequent use, voltage will be restored on the first charge and from then on they remain the same.


You refer to this dragging down but don't explain how this can happen. The self discharge rate of an older battery may be somewhat more than a new battery so if the discharge rate of the old one is twice that of the new one, then there will be current flow from battery to battery. But it is insignificant. If the discharge rate of the old battery 2% per month instead of 1%, that is 2amp-hours per month which calculates to 3 thousandths of an amp of dragging down instead of 1.5 thousandths of an amp.

There is some truth in this in the case of mixing lead-acid and sealed batteries. Once or twice a year you can remove the sealed battery and switch to lead-acid equalizing settings but to be honest, with over 50 years experience on charging and using batteries I've not seen any suddenly sulfate up because you limited maximum voltage to 14.2.

HUH??
WHERE IN THIS THREAD DID I MENTION BATTERY COMBINERS (apart from this line )?
I encounter resistance in these forums because I am a manufacturer and some resent the free advertising. But it so happens that I have over 50 years experience in these subjects so that is where I comment. You should be grateful that there is a manufacturer helping sort out the information here. You quote battery manufacturers with differing opinions. Where are THEY posting here? Do they not have a vested interest in selling their batteries?

I guess we needn't worry about equalizing batteries then even when their resting voltage and cells differ in spg by 2 or more points. It must just be the battery companies trying to get us to age our batteries fast so they can sell us some new ones

[btrayfors]

As per usual, Andina has a point. Or, maybe, two.

But also as usual, she goes too far.

In particular, in saying that mixing of battery types is OK.

This is patently WRONG. Especially when talking about mixing flooded lead-acid batteries with gelled lead-acid batteries.

Problem is, gels need to be charged at a fairly low acceptance voltage 14.1-14.2VDC. Flooded batteries, like the venerable T-105 Trojan, need to be charged at 14.8-15.0 volts. If you charge them at lower voltages, you will hasten the sulfation process.

Sulfation can and does occur at lower voltages than we usually think. For example, if you float your T-105s at 13.2-13.4VDC, they will sulfate. They need to be kicked up to absorption voltages (14.8-15.0VDC) frequently in order to allay the dreaded sulfation effects.

Furthermore, they need to be equalized periodically at 15.5 to 17VDC to knock the loose PbSO4 crystals off the plates. These voltages would kill a gelled battery deader than a doornail.

So....mixing flooded and gelled batteries is a BAD idea. I challenge anyone who has REAL DATA, not conjecture, to dissuade me from this belief.

By contrast, mixing AGM and flooded batteries may be OK. That's because the charging profiles of these types of batteries are virtually identical, differing by only 0.1VDC on some parts of the charging cycle. Both are pretty robust batteries.

Re: old and new batteries, with some exceptions, I would follow the advice of battery manufacturers, battery researchers, and virtually every professional in the business (except Andina) and stay away from this practice insofar as possible. Not to be paranoid about it, but just to try to not do it.

Why? Because an old battery with a greatly reduced capacity, will come to a "charged" voltage much faster than will a newer battery in good condition. This would raise the voltage of the bank as seen by the battery charger or alternator regulator and "trick" them into believing that the battery bank is more fully charged than it actually is. In other words, the newer batteries in the bank would always be "cheated" because the old battery bank's higher voltage would trick the charging source.

Is this a real problem? Maybe. Could it be? Maybe. As with most things, the answer is, "It Depends".

Bottom line: UNLESS YOU HAVE A VERY GOOD REASON NOT TO, TRY TO KEEP ALL THE BATTERIES IN A SINGLE BANK OF THE SAME AGE, SIZE, AND TYPE.

Bill