Battery Compatibility

[Pat & Pete]

Would a dual purpose AGM be compatible , connected in parallel , with a deep cycle AGM battery .

 

I know balanced is best , but ...

 

[Yarome]

It's doable. I wouldn't expect to get the rated capacities or the expected life cycles, but it would keep you running. It certainly won't harm anything. In that situation I wouldn't bulk charge over 14.4 or run an equalization cycle on a mixed bank. I getcha though.. sometimes you gotta make do with what's "on hand".

[Kirk W]

Do you already have both batteries and are using what you have, or would you be buying one of them new? I might do this with two old ones, but not with a new AGM.

[oldjohnt]

As you're already aware, but for others, for multiple battery use, its best if all batteries are matched as far as type, size, design, capacity and age WELL DUH as you don't want one battery cannibalizing another or other conflicts. That being said, sure it can "work" otherwise and even if not perfectly matched total energy storage can still be increased using more batteries. Another issue with multiple batteries is if they get charged at equal rates because it then even gets worse if one is at a lower charge state then another, yet the parallel connection dictates the voltages will be held the same.

 

Since you're connecting in parallel in theory the available cranking amps as well as the Amp Hours of energy storage IS ADDITIVE which is a good thing.

 

Not knowing everything about your batteries, here is a concern I have, although I cant say for certain how well its justified: I would be concerned if both batteries In parallel will receive an equal and sufficient charge??????? If not, then any mis match becomes more serious and one may be drawing the other down. The more the batteries are matched the less is my concern, while the more they are NOT matched my concern would increase. My old engineers brain just has a hard time envisioning that two different batteries in parallel (current divider) are both going to get the same charge current.

 

Its probably something I would NOT do, but hey its your money and your choice and YES amps and amp hours is still additive. I may be over worrying (I cant help it, its in my engineers brain DNA lol) any unequal charge due to the current divider method of parallel charging and before throwing a battery away or spending another $100, heck give it a try, but use a hydrometer to keep an eye on the charge states and as long as they remain the same in all cells on both batteries, you're likely okay..........

 

I guess if money was not an issue I wouldn't do it, but if it is, give it a try but monitor each cell and each battery so you will see what's happening.

 

John T

[Pat & Pete]

Gentlemen , Thank you for your comments / advice , so far .

 

I've learned a bit more information this morning . I'm working on this project for a friend and sometimes some things get 'lost' due to mis-communication or misunderstanding .

 

Anyway , the dual purpose AGM he currently has is about 6 months old and has had very limited use .

The deep cycle AGM is yet to be purchased or not .

I've found a dual purpose AGM that could be bought instead , but it has a lesser amp / AH rating . I'm thinking that even though the 'new' dual purpose has a lesser rating , the system would be better , both now and in the long run .

 

The batteries would be connected via 4 gauge or possibly multiple 10 gauge . The 10 gauge is what he has a lot more than enough of . Maybe that doubled or even tripled would be sufficient ? The distance between batteries looks like it will be just about 9 feet .

[oldjohnt]

I prefer the two more similar (you call dual purpose) batteries in parallel then two different (one deep cycle battery one dual purpose battery) even with slightly different amp hour capacities on the two.

 

If I had my druthers, for deep draw down and RV use, ID OF COURSE PREFER TRUE DEEP CYCLE BATTERIES versus what you call dual purpose. I call such batteries "semi deep cycle" or "quasi deep cycle" like sold and labeled at Wally World as RV/Marine batteries.

 

I DO NOT (for several reasons) prefer multiple conductor say 10 Gauge wire use as opposed to simply bigger wire like 4 gauge etc.

 

When connecting batteries, try as best possible for same wire and same wire lengths. IE the parallel ties from + to + and - to - should be same size and length.

 

When you connect the Pos and Neg wire runs from the two battery combination to the load, connect the + to one battery and the - to the other battery.

 

We report you decide

 

John T

[oldjohnt]

PS My bad, I see you are using AGM so forget what I said about a hydrometer, but my other concerns remain valid and AGM are sensitive to correct charging which increases my equal charging concerns if batteries are mis matched.

 

John T

[Ray,IN]

I prefer the two more similar (you call dual purpose) batteries in parallel then two different (one deep cycle battery one dual purpose battery) even with slightly different amp hour capacities on the two.

 

If I had my druthers, for deep draw down and RV use, ID OF COURSE PREFER TRUE DEEP CYCLE BATTERIES versus what you call dual purpose. I call such batteries "semi deep cycle" or "quasi deep cycle" like sold and labeled at Wally World as RV/Marine batteries.

 

I DO NOT (for several reasons) prefer multiple conductor say 10 Gauge wire use as opposed to simply bigger wire like 4 gauge etc.

 

When connecting batteries, try as best possible for same wire and same wire lengths. IE the parallel ties from + to + and - to - should be same size and length.

 

When you connect the Pos and Neg wire runs from the two battery combination to the load, connect the + to one battery and the - to the other battery.

 

We report you decide

 

John T

12V batteries must be connected in parallel, 6V are connected in series. The OP has 12V, connecting them in series makes a 24V system.

[oldjohnt]

Ray, you state: "12V batteries must be connected in parallel, 6V are connected in series. The OP has 12V, connecting them in series makes a 24V system."

 

I AGREE, YES you're correct, for twelve volt operation if he has two twelve volt batteries, they must be connected in parallel and as I told him ".....When connecting batteries, try as best possible for same wire and same wire lengths. IE the parallel ties from + to + and - to - should be same size and length."

 

I don't envision him wiring them in series for 24 volts at all.

 

I also told him ".....When you connect the Pos and Neg wire runs from the two battery combination to the load, connect the + to one battery and the - to the other battery"

 

For two parallel battery configurations, when you connect the outgoing load wires the system is better balanced if the + outgoing lead is on one battery and the - outgoing lead is on the other battery. When done that way the loads as well as charging current is better balanced then if you took the + and - just off one battery. Although its slight, there is some resistance in those parallel tie wires, so if you connect as I just stated the resistances are equal assuming BOTH parallel tie wires (+ to + and - to -) are equal.

 

I think we have beat this to death lol here is more information regarding even better parallel battery connections, although the above is still better then just using one battery for the final load connections:

 

http://www.smartgauge.co.uk/batt_con.html

 

Take care and safe travels yall

 

John T

[Pat & Pete]

Gentlemen ,

 

Thank You , once again .

 

And , you're right , John T . 12 volt only . No need for 24 volt .

I'm aware of the effect of series connections produce ( 6 > 12 > 24 etc ) .

 

Anyway , the closest match battery has been ordered , along with matching connectors .

I'll have to run a little extra cable to get balance as best we can , but , I guess that's the price .

 

Someone once told me that it only cost a nickle more to go first class .