Two different CCA - Dual Battery (1 Viewer)

[Mixelplix]

Now that my 91 isn't my daily driver, I want to go ahead and do some projects I intended to do.

My first project is a dual battery using the blue sea relay.

I'm reading on several plow related sites that the batteries shouls be the same size (in CCA), and the same age. Any truth to that? I intended to use a 850CCA lead acid battery I have from a previous vehicle in conjunction with the AGM starting battery (Autozone group 31, maybe?) that's currently in it.

Am I in for trouble?

 

[Cruiserdrew]

No, won't matter a bit. If they were in a bank, together, then definitely same matched batteries are important, but in a relay based system like the Blue Sea (which is excellent IMHO-I have 2 trucks running an ACR) as soon as the input drops below 13volts, it will separate the batteries, so no concerns.

I'd try and have a deep cycle capable battery for the #2 battery if you plan to run loads like refrigerator or similar.

Which Blue Sea relay? 7610 or 7622?

 

[Mixelplix]

Thanks for the information!

I believe it's the 7610, I remember paying $75 - $80 for it.

I intend to get a deep cycle at some point, but for now I just want to get the project started.

 

[JCruse]

Well that sure is good news. I bought a group 31 - 2150 amp (1150CCA) Odyssey last year when someone had them for $260, but now that they're all $350 and up I wasn't too happy about having to buy another. However I have heard what the OP said about matching batteries here on Mud many many times. Why the confusion?

 

[bricat]

I have had 2 batteries purchased at the same time, same CCA, fail at exactly the same time. (happened twice; once in boat) I think buying batteries 6 months apart may allow the second battery not to fail at the same time. I realise load, charging, heat etc play an important part in battery longevity. but I will not buy 2 batteries for the same project at the same time. JMHO cheers Brian

 

[1973Guppie]

It really depends on your dual battery setup. I am using the blue sea unit and it connects the batteries during driving so that they will be charged by the alternator. I already have gone through one battery because of this as one of the batteries was purchased earlier than the other. I plan to eventually purchase 2 of the same deep cycle batteries at the same time to install into the truck.

 

[Brentbba]

I just replaced a 5 year old Sears Platinum that had a little life left and a 7-8 year old Optima Yellow top that was dead as could be with two brand spanking new Odyssey AGM batteries. That tandem worked for the 5 years I had it. Can't remember the separator I use. Automatic functionality.

 

[mickeyt]

Is this overkill?
Odyssey PC2150T Dry Cell AGM Battery
https://www.google.com/shopping/pro...kBA&ei=ODFIVbPWEsiYsAXQ5oDQCw&ved=0CH4QpiswAQ

 

[Brentbba]

Damn - will that monster even fit in the battery box? I think mine were the group 31. Whatever the Odyssey site said would fit the LC.

 

[Mixelplix]

That's a big boy.

 

[oilbrnr]

I personally would not worry about the CCA, but type and age/usage I sure would...

 

[Cruiserdrew]

It does not matter. The only time it matters is in a battery bank situation where 2 or more batteries are paralleled. Like an RV or Boat battery bank. Then if one battery is "weaker" is could theoretically drain the "stronger" battery.

In a split charging system, the batteries get fully charged when the truck runs or shore power is applied. Once the charge voltage is removed, the batteries float at surface charge for a brief bit but as soon as they hit resting charge-roughly 12.8 volts, the relay will open and there is no connection between the batteries. The Blue Sea has some time delays built into the circuitry, but put your volt meter on your batteries and see the behavior for yourself.

The same is true for a mixed system, like 1 AGM battery and 1 Flooded Lead Acid (FLA) battery. They do charge differently, but they rest at about the same voltage, which is below where the relay will open, separating the batteries.

The matched battery thing is only important in a paralleled battery bank. For our purposes it does not matter.

 

[1973Guppie]

It does not matter. The only time it matters is in a battery bank situation where 2 or more batteries are paralleled. Like an RV or Boat battery bank. Then if one battery is "weaker" is could theoretically drain the "stronger" battery.

In a split charging system, the batteries get fully charged when the truck runs or shore power is applied. Once the charge voltage is removed, the batteries float at surface charge for a brief bit but as soon as they hit resting charge-roughly 12.8 volts, the relay will open and there is no connection between the batteries. The Blue Sea has some time delays built into the circuitry, but put your volt meter on your batteries and see the behavior for yourself.

The same is true for a mixed system, like 1 AGM battery and 1 Flooded Lead Acid (FLA) battery. They do charge differently, but they rest at about the same voltage, which is below where the relay will open, separating the batteries.

The matched battery thing is only important in a paralleled battery bank. For our purposes it does not matter.

I was under the impression that the blue sea unit I am running simply connects the 2 batteries after the vehicle has started and disconnects them after it has been turned off. Wouldn't this process cause the batteries to be connected during vehicle operation and thus be susceptible to not being matched and draining each other?

From my experience some battery managers are "smart" (like my old painless wiring unit) and will delegate voltage to the battery that needs it, etc and others (like the blue sea) are simply voltage readers that open and close the relay as per my comments above.

Always learning, learning, thx for the clarification. For the purpose of discussion here is the one I am using, and btw I love it, very nice operation and quality!:

http://www.amazon.com/Blue-Sea-Syst...&qid=1430884828&sr=8-1&keywords=blue+sea+7622

Noah

 

[Douglas S]

I was under the impression that the blue sea unit I am running simply connects the 2 batteries after the vehicle has started and disconnects them after it has been turned off. Wouldn't this process cause the batteries to be connected during vehicle operation and thus be susceptible to not being matched and draining each other?

From my experience some battery managers are "smart" (like my old painless wiring unit) and will delegate voltage to the battery that needs it, etc and others (like the blue sea) are simply voltage readers that open and close the relay as per my comments above.

Always learning, learning, thx for the clarification. For the purpose of discussion here is the one I am using, and btw I love it, very nice operation and quality!:

http://www.amazon.com/Blue-Sea-Syst...&qid=1430884828&sr=8-1&keywords=blue+sea+7622

Noah

The Blue Sea connects and disconnects based on voltage. If either of the batteries is above a certain voltage threshold (IIRC above 13V for 90sec or 13.5V for 30 sec), then the solenoid closes and connects the batteries. When voltage drops below 12.75V they are disconnected.

The batteries are only connected when charging or above 12.75V so there is no way for them to drain each other. Thus there are no issues with battery compatibility.

 

[1973Guppie]

https://www.bluesea.com/products/76...rging_Relay_with_Manual_Control_-_12V_DC_500A

please see above link, this clearly states that the unit automatically combines the batteries during charging. Thus if you camp all night and your house battery drains to nothing, upon startup (after a few moments) the acr will connect and combine the two batt's thus having the situation of one batt having no charge and one having a full charge (starting batt) thus the issue of combining non similar batt's and / or different aged batt's comes into play. It also clearly mentions that it allows paralleling of battery banks for emergency starting, which is basically just a switch which allows you to overide and do the manual process via the switch that the acr would do on it's own automatically.

Am I missing something? wouldn't be the first time that is for sure, lol

 

[Cruiserdrew]

Yep, you're missing something. The something, is that during the time it matters, ie not being charged but in use, the batteries are not connected. When being charge there is a huge excess of charging current at the voltage set by the alternator. The batteries are never not being charged, and paralleled.

During engine on charging, there is way excess voltage and current, to overcome any possibility of discharging into one or the other.

Seriously, your voltmeter and 15 minutes will illustrate all.

 

[1973Guppie]

Yep, you're missing something. The something, is that during the time it matters, ie not being charged but in use, the batteries are not connected. When being charge there is a huge excess of charging current at the voltage set by the alternator. The batteries are never not being charged, and paralleled.

During engine on charging, there is way excess voltage and current, to overcome any possibility of discharging into one or the other.

Seriously, your voltmeter and 15 minutes will illustrate all.

ok, I get what you are saying, basically during charging even though they are connected they don't discharge to each other as there is active voltage going INTO each battery?

what about the scenario where you are using the switch to combine the 2 batteries when the engine is off in an emergency situation?

 

[george_tlc]

While the engine is running the alternator/regulator puts out HIGHER voltage than either 'mismatched' battery rests at - so they are both charging and it makes no difference if one is older/weaker/sad/unhappy etc versus the other.

If you manually combine while the engine is off then the two batteries will balance out voltage wise, basically one battery will 'charge' the other until they reach a balance. Considering the only reason to combine the two batteries is to jump start yourself and after that the alternator is charging everything again.

As cruiserdrew mentioned, the way we use the batteries (combined while charging and separated the rest of the time) there's no issue with 2 different capacity/age batteries.

cheers,
george.

 

[Mixelplix]

This has been extremely informative. Thank you.

 

[1973Guppie]

well I spoke with Blue Sea about this topic and they confirmed that matching types of batt / age does matter as far as the life of the batteries is concerned. They confirmed that one batt will drain the other based on how the blue sea switch operates.

Based on their expertise I will be installing matched deep cycle batteries from costco soon. I have already had one battery go bad due to the above reasons.

As far as reliablitity goes, I have to disagree with you guys and that it does in fact matter to have matched age/type of batteries when using the blue sea switches and in order to get the most reliable setup I would suggest to others to do the same. Of course no ill effects will come to the actual blue sea switch but only to the life of the batteries themselves from being discharged or equaling themselves out.