Gel batteries and lead acid batteries on line?

[dnej]

Is there any complication with putting a gel battery and a lead acid on line together. What do we need to do, anything special?
David

[driveon]

Hi again dnej, gel batteries and lead acid batteries are the same thing.

I think what your trying to compere is gel cell batteries and flooded wet cell batteries and to your question, there is no reason for not connecting the two types of batteries in parallel.

The only thing to watch out for, is when you have to select the voltage level that you want a battery charger to charge the batteries at.

Because the gel cell has a lower maximum tolerable charging voltage ( usually no more than 14.4 ) you must make sure the charger is set to this maximum and DO NOT use an Equalising or Boost mode with the gel cell ( or for that matter not with an AGM either ).

[foxx510]

Do you have the make/model of the batteries you are talking about? A standard flooded lead acid(car battery) can tolerate a much higher charge/discharge current than a sealed "gel cell" battery. I wouldn't be connecting them in parallel personally.

[dnej]

foxx510 and driveon,
That is the information I was after,yet we have conflicting responses. I will find out more about the models, and get back to you
Thanks
David

[foxx510]

The problem will be the potential for massive current flow when the batteries are at different voltages and one tries to charge the other. You might be able to buy a battery management system that fixes that problem.

[driveon]

Hi dnej and fox, the first time you connect them, if they are at different States of Charge then there will be an “equalising” of the voltage levels but even if you had two identical types of batteries with different SoC, the same thing would happen so there is no real difference as to the whether the two batteries are the same or not.

Further more, if you are charging these two batteries, once connected in parallel, using an alternator, then the current from the alternator will be high enough to keep the voltage at both batteries higher than the State of Charge of either battery so there will be no flow of current from one battery to the other.

Last but not least, even when connecting any form of batteries in parallel, once they have reached the same State of Charge, whether it be by one battery discharging down to the other or by both batteries being fully charged, provided they are left permanently connected together, they will charge and discharge at the same level all the time and will act as one large battery.

[TheRealAndy]

Hi dnej and fox, the first time you connect them, if they are at different States of Charge then there will be an “equalising” of the voltage levels but even if you had two identical types of batteries with different SoC, the same thing would happen so there is no real difference as to the whether the two batteries are the same or not.

Further more, if you are charging these two batteries, once connected in parallel, using an alternator, then the current from the alternator will be high enough to keep the voltage at both batteries higher than the State of Charge of either battery so there will be no flow of current from one battery to the other.

Last but not least, even when connecting any form of batteries in parallel, once they have reached the same State of Charge, whether it be by one battery discharging down to the other or by both batteries being fully charged, provided they are left permanently connected together, they will charge and discharge at the same level all the time and will act as one large battery.

Two different chemestries means they will never charge and discharge at the same rate. Keep them seperated with a charger or VSR.

[driveon]

Two different chemestries means they will never charge and discharge at the same rate. Keep them seperated with a charger or VSR.

While this is sort of true, they are all lead acid batteries, it’s just the way they are constructed that makes one type of battery different from another.

It’s only relevant in high current situations such as those found during vehicle winch operations, where batteries should be identical, otherwise there is no difference in the way any type of 12 volt lead acid battery works.

I’ve been supplying dual battery systems for over 20 years and have thousands of customers, most of whom have dual battery set ups using dissimilar batteries and have never had a customer report any form of problem relating to using dissimilar batteries.

[foxx510]

Normal starter batteries are designed to have a shallow discharge and a high current recharge, whereas most gel batteries are designed for a deeper discharge and a slower charge. Most normal gel batteries won't tolerate repeated high starting currents either. I'm sure the is are odd cases where you might get away with it with certain batteries, which is why I asked for the make/model numbers. Otherwise I'll stand by my opinion of it being a bad idea.

[driveon]

Hi again Fox, and I know what your trying to say but you are still misunderstanding battery types.

The most common type of battery, both as a cranking battery and a deep cycle battery is a flooded wet cell battery. These batteries are easily identified by the screw type filler caps on top of the battery.

There are maintenance free batteries which are similar to flooded wet cell batteries but instead of being filled with a fluid electrolyte, the electrolyte is in a gel form and the battery does not have easily accessible filler caps, in other words, the battery is sealed.

Most gel cell batteries are cranking type and are not all that good as deep cycle batteries.

The third type of battery is an AGM battery and there as many types of these as there are brands and like the gel cell batteries, AGMs are sealed.

Most AGM batteries are intended for deep cycle use and not for cranking.

So you need to know exactly what type of batteries they and even then, if being used for deep cycling, any of the batteries can be wired in parallel.

From dnej’s original question, if they are as he posted, a gel and a flooded wet cell, then they are most likely crankers and can also be wired in parallel for cranking use, but until he posts the exact type and his intended use, we wait.

[foxx510]

Yep I see your point. When someone says "gel" battery I usually assume "deep cycle".

What I'm getting at is that without knowing what he's got there I'm still hesitant to say it would be ok. There's every chance his outboards charging circuit will go above the safe 14.3v too.

[TheRealAndy]

I am not going to get into a protracted argument about this but a liquid and a gel are considereded different chemestries. They are clearly different, I think its fairly obvious.

IF in doubt, seek manufacturers advice. They will tell you the difference.

[driveon]

I am not going to get into a protracted argument about this but a liquid and a gel are considereded different chemestries. They are clearly different, I think its fairly obvious.

IF in doubt, seek manufacturers advice. They will tell you the difference.

Hi Andy, could you post a link to any one of the battery manufacture’s web sites where it specifically states that these batteries are chemically different?

[TheRealAndy]

Hi Andy, could you post a link to any one of the battery manufacture’s web sites where it specifically states that these batteries are chemically different?

Ring the manufacturers and they will send you some data, but chances are they wont reveal the exact chemical composition as its the same as you revealing your secret fishing spot. Searching patent records would probably be more sucessfull. I am sure if you spent hours trawling through data sheets on the big manufacturers you might find something, but I have better things to do with my time. For the record:

• Flooded wet cell typically uses sulphuric acid and Water but may also have other chemicals added.
• Gel cell uses (from memory) sulphuric acid, water, fumed silica and another acid(I think phosporic). I have read in engineering journals about some newer polymer gels but I presonally dont know anything about them.
• Both types of batteries also typically use different alloys in the manufacuting of the plates.

Furthermore, a gel cell is recombinant, a flooded battery isn't.

[driveon]

Andy, all automotive batteries require sulphuric acid and water as the primary chemicals.

The major difference between the different type of automotive batteries is in the way they are constructed, this is where the will major variants in charging, discharging and storage capabilities of the different types of batteries can play a part in how they should be used.

While most automotive battery situations DO NOT require the use of identical batteries, to be able to be wired in a parallel configuration, as foxx510 has posted, until dnej posts up what he intends to do, this whole thread is academic.