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Why do the dual battery mod?

Chaos67731

Full Member
Joined
Mar 18, 2015
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42
I have seen a few post about doing the Dual Battery mod, and watched a few videos on it. . It seems like a simple thing to do, but I dont understand the point of it. 

What does it help with?

- I have a 2003 2500 :)
 
If your pulling more power with lights and a winch like I am on my truck I really think I'll end up doing it soon.
 
Also , with this mod. . . is there any way to make it so the radio does not turn off when you start the truck. 

I was in a car the other day that did not do that and it was nice.
 
guys do it for a few reasons. some guys like to have it as a backup battery, so they wire in an isolator so in case their battery goes dead, they flick a switch and they're good to go. some use it for tailgateing. want longer play times or have accessories pluged in type thing. I have it because of my stereo. I have a lot of power so I need the extra battery bank. not everybody needs to do it. it all depends on how much power you use....... as fo radio staying on I've never heard of it so ya got me.
 
While many people do two batteries for many different reasons there are really only 2 valid reasons for the vast majority of people to run two batteries.

Remember, Batteries store power, alternators make it...  But you need a battery connected to an alternator because the battery smooths out the alternators output so NEVER try running your vehicle or components directly off an alternator with no battery or you can cause damage due to the raw alternator output.

So the valid reasons are:

#1, you power equipment with the vehicle off and want to be able to insure you can start the vehicle once you killed the battery you are running your equipment from.

#2, you have multiple alternators such as for a very large sound system etc.. You should have a battery on each alternator to smooth out its output. Capacitors are sometimes used but Alternators are designed to charge batteries, not run systems directly.

Rodney
 
redheadedrod said:
While many people do two batteries for many different reasons there are really only 2 valid reasons for the vast majority of people to run two batteries.

Remember, Batteries store power, alternators make it...  But you need a battery connected to an alternator because the battery smooths out the alternators output so NEVER try running your vehicle or components directly off an alternator with no battery or you can cause damage due to the raw alternator output.

So the valid reasons are:

#1, you power equipment with the vehicle off and want to be able to insure you can start the vehicle once you killed the battery you are running your equipment from.

#2, you have multiple alternators such as for a very large sound system etc.. You should have a battery on each alternator to smooth out its output. Capacitors are sometimes used but Alternators are designed to charge batteries, not run systems directly.

Rodney
Would it be safe for me to hook up two batteries off one alternator?
 
Dakotawilk said:
Would it be safe for me to hook up two batteries off one alternator?

Most certainly. That is how my truck is setup. You MAY want to go to the bigger 145 amp OEM alternator or a built aftermarket if your accessories are pulling too much but you can certainly drive more than one battery off one alternator. Only time you really see multiple alternators is for really big systems or someone got a secondary alternator for a great price and want to use it instead of buying an expensive aftermarket.

A battery isolator of some sort is necessary if you want to separate the batteries to protect your main system battery to be able to start your truck. That is the reason for the painless wiring kit. Your alternator will see the "most charged battery" and charge according to it so it is important to use matched batteries.

When you go to a two battery system I would strongly suggest just getting two good quality standard batteries. Optima batteries and other third party batteries are overkill for 98% of the people out there...

Rodney
 
I went to 3 on my AV.
Stock then Audio & electronics, and then Flexolite fans, trans cooler fan, winch, air compressor, self jump.
also a 250Amp alt
 
redheadedrod said:
Most certainly. That is how my truck is setup. You MAY want to go to the bigger 145 amp OEM alternator or a built aftermarket if your accessories are pulling too much but you can certainly drive more than one battery off one alternator. Only time you really see multiple alternators is for really big systems or someone got a secondary alternator for a great price and want to use it instead of buying an expensive aftermarket.

A battery isolator of some sort is necessary if you want to separate the batteries to protect your main system battery to be able to start your truck. That is the reason for the painless wiring kit. Your alternator will see the "most charged battery" and charge according to it so it is important to use matched batteries.

When you go to a two battery system I would strongly suggest just getting two good quality standard batteries. Optima batteries and other third party batteries are overkill for 98% of the people out there...

Rodney

Would a stereo shop be the best place to get a 2nd battery installed? I just got my truck with a little under 100K miles on it. Good idea to get 2 new batteries?
Thanks,
 
All depends on what you want to do... For a normal person with no extra accessories, a waste of money...

Someone that has a little more powerful system, some lights or something else...
Bigger alternator makes more sense.

If you are doing a big system or have other things that will draw power or you want to have extended listening time on your stereo without worrying about making it so your truck don't start then it makes sense. Or if you add more alternators. You can always run more than one battery off an Alternator but you must always have atleast one.  When you have more than one you really should have some sort of isolation mechanism. You can go with a Diode setup but that will reduce the charging voltage to your battery, a solenoid made for full duty service that is only connected when the truck is running, or an all digital system.

I now have 2 batteries in my truck using 2 separate alternators.
 
You can, the weaker battery can put a strain on the other and can also strain the charging system.
There are a lot of variations depending on load usage and charging. It?s not the age.
The difference in condition of the two batteries.

  So they may last or may not. I put a 7 year Die Hard in on my first set up ($$$). With a PainLess controller.
You do need some kind of controller/isolator. I can?t remember how long they lasted. Then I went with two twin batteries.
Also best to stay with twins same series, with wet, AGM, or Gel.
 
Depending on how you are charging them it can make a difference. If you have one alternator charging both batteries and you are using a solenoid which basically connects them together all the time when the truck is running then you need closely matched batteries. Otherwise one of the batteries will likely never get full charged because the smaller one, or more worn one will likely show the system full voltage long before the new battery has a full charge and will basically prevent from charging.

Especially with newer trucks that tend to throttle the alternator when the battery is fully charged.

Your best bet if you are not using matched batteries is to use a (expensive) digital system that will monitor the batteries and just charge the one that needs it.

Rodney
 
I have the older Marine Switch I bought at West Marine...I like to use it unless simpler method. I could charge battery separately on 1 or 2 would that avoid the issue with one bringing down the other? I used this switch for my 2 battery banks on motorhome with solar panels, worked out very well and put catastrophic fuse inline
 

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redheadedrod said:
Depending on how you are charging them it can make a difference. If you have one alternator charging both batteries and you are using a solenoid which basically connects them together all the time when the truck is running then you need closely matched batteries. Otherwise one of the batteries will likely never get full charged because the smaller one, or more worn one will likely show the system full voltage long before the new battery has a full charge and will basically prevent from charging.

Especially with newer trucks that tend to throttle the alternator when the battery is fully charged.

Your best bet if you are not using matched batteries is to use a (expensive) digital system that will monitor the batteries and just charge the one that needs it.

Found this setup... https://andyarthur.org/dual-battery-setup-on-my-silverado-for-camp-power.html

Rodney
 

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That's how mine is setup up, I installed it in 2004 if I remember correctly when the battery was my AV was almost 3 years old.

I have a dual battery wiring kit from Wrangler, the Painless kit is pretty much the same. It has saved me from calling a tow truck for a jump or flagging down someone a few times when my AV has been sitting for a few weeks without starting.

How it works and wired (crude drawing) plus Big 3 plus..

Position 1 on the switch - Battery connected when ignition is turned on, both batteries charge when running. Batteries disconnected from each other when ignition is off and anything connected to aux battery does not drain the main battery.

Position 2 on the switch - Batteries isolated/disconnected from each other only main battery chargers when running. 

Position 3 on the switch - Batteries connected ignition on or off, both will charge when running, both will be used for whatever load is connected to either. In this position is also how to jump start yourself if your main battery is discharged providing you do not have load/drain on your aux battery.

Edit.. I also installed a Powermaster 225 amp alternator and upgraded the charge cable from the battery to a 1/0.
 

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Randy said:
That's how mine is setup up, I installed it in 2004 if I remember correctly when the battery was my AV was almost 3 years old.

I have a dual battery wiring kit from Wrangler, the Painless kit is pretty much the same. It has saved me from calling a tow truck for a jump or flagging down someone a few times when my AV has been sitting for a few weeks without starting.

How it works and wired (crude drawing) plus Big 3 plus..

Position 1 on the switch - Battery connected when ignition is turned on, both batteries charge when running. Batteries disconnected from each other when ignition is off and anything connected to aux battery does not drain the main battery.

Position 2 on the switch - Batteries isolated/disconnected from each other only main battery chargers when running. 

Position 3 on the switch - Batteries connected ignition on or off, both will charge when running, both will be used for whatever load is connected to either. In this position is also how to jump start yourself if your main battery is discharged providing you do not have load/drain on your aux battery.

Edit.. I also installed a Powermaster 225 amp alternator and upgraded the charge cable from the battery to a 1/0.

It's nice to see someone else that did this setup...I was leaning towards this with a marine switch if need be! 
Regarding what you mentioned your Avy Battery was 3 years old...Was your second add on battery BRAND NEW? If so no issues with the two when charging at the same time AS mentioned by
redheadedrod : one of the batteries will likely never get full charged

1/O ???
I kinda remember hooking up my battery banks in parallel and in series to make sure they charge each to the fullest as well as discharging when in use! But then I was dealing with 6 volt deep cycle batteries tied together to make 12 volt system on motorhome!
 
That's why I waited until it was almost 3 years old, that's how long most stock batteries have lasted me in the past. I put in two new batteries at that time and two new every 8-9 years (about how long Optimas have lasted) because you should use matched size and age or you may run into problems, as a matter of fact I'm about due for new batteries now, they are 8 years old. Some don't like the Optimas but they have worked fine for me..

I did not want to use a marine battery disconnect since you would always have open the hood to switch batteries and they are pretty big so finding a place to mount one can be difficult. And yes the batteries will be hooked up in parallel..
 
When you use batteries together like that they SHOULD be very similar batteries. Doesn't matter how you connect them because the weakest batteries will charge first and tell the charging system they are charged thus never fully charging the stronger batteries. NEVER mix a deep cycle battery and a standard battery. They MUST match in type and approximate age or you will have issues or a shorter life span than normal for one of the batteries.

Series batteries provide double the voltage...  But if you are using 2 batteries of different capacity or age where they are measurably degraded you will never fully charge the good batteries thus reducing their life dramatically.

If you do them in parallel they generally double the storage capacity. But again the batteries need to be similar in type, size and age.

If you decide to use a deep cell battery and a standard battery you must use a digital style charging system or you will reduce the life of one of the two batteries. Which one will depend on their characteristics. Other option is a separate alternator for the deep cell battery.

 
It is possible to run two batteries without connecting them in parallel and having them matched, you just need a DC isolator. like this:
https://www.renogy.com/200a-battery-isolator/?gclid=Cj0KCQiAuefvBRDXARIsAFEOQ9FI0Iwil4bXplTnTd36oS_oP7h_lZt5qJwaGzyuqQxz-tC6tQt1-eoaAh1XEALw_wcB
I ran a dual setup with mismatched batteries of different age (roughly two years) for almost three years with no issues using a Renogy isolator before switching to  a twin alternator four battery setup in my 08'.
one of the batteries from that system is still in use (now in my 13') 7 years later.
Is it ideal to have matched units, absolutely, not it is not necessary if you use an isolator.
 
Yes you can run different battery size and age when using an isolator. You can have a main starting battery and second bank or banks of batteries. The isolator monitors each bank and chargers each on what amount of charge is needed. If you need to jump start the vehicle you will need to use jumper cables or a battery switch that would tie them together temporally to do so.

In a system such as mine, it is not advised and the batteries should be matched size and age.. With that said if you are using an isolator and one or more of the banks have more that one battery, each bank should be matched for the best performance.

 
Randy said:
>:D
If you need to jump start the vehicle you will need to use jumper cables or a battery switch that would tie them together temporally to do so.
Correct, but the  looks you get  ??? when you pull out jumper cables and have both ends under one hood are priceless though.
 
I just have a 250 amp breaker between my alternators... If I need to give myself a jump I just close the breaker and jump it then open the breaker back up. No jumper cables required... ;)
 
Can someone lend me some help have 2005 suburban 2500 wanting to do the dual battery for radios and such.i have the connector hanging on firewall it doesnt have power have checked with test light.i know goes to the under hood fuse box.can someone help me figure out how to get power to this connector?i want too keep it factory and wire for rpo tp2 option
 
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