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Dual battery/isolated batteries/winch/welding

149970 Views 171 Replies 49 Participants Last post by  Daing_Maing

The most simple reason for dual batteries is better starting and the ability to go farther if your charging system quits working.

This is the 'Correct' way to wire up Simple Dual Batteries.
It is VERY simple to do, will more than double your ability to get back to a parts store if your charging system quits working



This is a Upgrade to that first, Simple diagram that allows you to remove one battery at any time for field service, camp site chores, to 'Lend' power to someone that needs it so you don't have to stay and wait to jump start them when they are done 'Fiddling' around, ect.

Link to graphic:


The next 'Upgrade' when you have dual batteries is to Isolate the second battery from accidental discharge.

Most of the time it's done INCORRECTLY with a 'Continuous Duty' Relay ('Solenoid') between first and second battery.


Link to graphic:

Most aftermarket 'Kits' for dual batteries do things this way, and it's most certainly NOT the way to go if you intend to have full use of the second battery.


This is the next step up in dual batteries with 'Isolated' second battery.
The second battery is ISOLATED, so if something runs your primary battery down when the engine isn't running, you will be able to 'Self Jump Start'.
This system also DOUBLES the current to your starer, making for much faster starts and allowing you to use the starter to get yourself out of situations where the engine won't run...

Link to Graphic:

It's a little more complicated than the simple cross over solenoid, but it works SO MUCH BETTER!


Power Relay for charging is a 70 Amp relay used for electric air compressor,
Starter 'Solenoid' for Harley Davidson Motorcycles, ect. so it's a common item that can be had with little or no effort.

The oil pressure switch is a factory Jeep unit used on the electric choke circuit,
You can get one from about any Chevy engine for the same purpose (Electric Choke and 'Idiot' light.

Chevy Truck Oil Pressure Switch For Electric Choke & "Idiot Light", around $5 from any parts store.


The LAST Graphic for this series of simple Dual Battery arrangements is a Dual Battery ISOLATED with 'Lend Power'.

By making a quick release battery mount (Fabrication) you can pull a battery for use anywhere you can carry a battery. Great for jump starting another vehicle when your Jumper Cables won't reach or use in the camp...

Link to graphic:

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Discussion Starter · #2 ·

This installment covers SIMPLE WINCH with Dual Batteries.

Winches will draw 500 to 700 Amps (Amperes) of DIRECT CURRENT when in 'Full Pull'.

There is no generator/alternator out there that would produce that much DC energy to power the winch directly.
It would take a separate V-8 engine and a DC generator the side of that V-8 to produce that 500 to 700 Amps directly.

Not very practical to tow around an 800 pound engine and 2,000 pound generator everywhere you go!

Enter a second battery...
The idea behind a second battery is four fold.

1. Batteries store a tremendous amount of energy that is fairly quickly released, more than any automotive charging system can produce.
A second battery will increase your 'Winch' time by supply the current needed by the winch motor,

2. A second battery will keep the first (Primary) battery from discharging to the point it gets damaged.
Batteries heat up during discharge, and if you 'Pull' on one too hard, the plates will heat up and warp, touch each other, and run the battery.

3. Batteries CHARGE SLOWLY, they don't like 'Fast' or high amperage charging, so the output from the vehicle factory charging system is PLENTY to charge both batteries over time after you discharge them while winching.

4. A second battery will leave you with enough energy to start the vehicle when you are 'Un-Stuck'.
Batteries recover very quickly, and a second battery DOUBLES your starting reserve as they recover.
('RECOVER', continue to convert chemical energy stored in the battery to electrical energy after you stop winching or welding, ect.)


The one thing to remember here is BATTERY CABLE SIZE TO THE WINCH!
The winch will REQUIRE more current than the starter motor,
So you MUST use larger cables to any connection to the winch.

Starters will normally run just fine in 4 AWG (American Wire Gauge) cables,
While most winches will draw upwards of 500 Amps in full pull,
So that cable size should be no less than 2 AWG in size.

I normally OVERSIZE the cables to the winch. 'Small' cables OVERHEAT when used hard, so oversizing the cable size is cheap insurance.

Link to graphic:

Keep in mind that WELDING CABLE is FINE STRAND wire with better insulation for this application.
Fine strand wire conducts more current, and it's easier to work with.

Welding cable has better insulation for this application than 'Automotive' wiring with vinyl insulation and thick strands.

Welding cable has a rubberized insulation that is better with grease/oil/chemicals, is better with abrasion resistance and is pretty good with UV (Ultra Violet, Sun Light) than vinyl insulated wire.


THIS DIAGRAM is the 'Simple' way to wire up Isolated Batteries with a single winch set of Solenoids/Controller.

The Third 'Starter' type solenoid connects both batteries together when you want to use the winch, no matter if the engine is running or not.

Link to graphic:


Some EXTRA redundancy, if you forget to turn switches off, have kids that play in the vehicle,
Have buddies that 'Fiddle' with things...


· Premium Member
11,200 Posts
Discussion Starter · #3 ·
"ULTIMATE" Redundancy, Isolation, Winch Install, Welding, Ect.

"Full On", Dual Battery, Dual Starter, Dual Winch Solenoids with ISOLATION of the second battery when the engine IS NOT running is a little difficult to do...

The Dual Starter Solenoid, Isolated battery part is pretty easy, and covered above.
But Going full on with Dual Isolated Batteries and getting the winch to work on demand, even when the engine IS NOT running is more difficult.

[B]This particular Graphic allows me to [U]'LEND POWER', WELD, ISOLATES BATTEREIS, WINCHES WITH ENGINE NOT RUNNING[/U] and does it all quite well![/B]

Link to Graphic: [URL][/URL]


The chances of your winch relays quitting are slim, but this DOES supply full current to the winch from BOTH batteries since there are direct leads from both,
And the winch solenoids are backed up by a second set,
So one battery and one set of winch solenoids will work even if the second is broken or removed.

It addresses the primary problems I run into once in a while.
With welding 'Yoke' below, jumper cables with Anderson Connector, and some welding rods or spool gun MIG welder I'm off to the races with about anything I face.

This may SEEM like a lot of wiring, but it's actually not compared to what your vehicles have right now, and not nearly as much as modern vehicles have!

· Premium Member
11,200 Posts
Discussion Starter · #4 ·
Making your system more 'USABLE'...

Using High Amperage transfer connectors, like the Anderson connectors I use (Dirt cheap all over E-bay) You can modify your system to 'Lend Power', Have quick disconnect Jumper Cables,
Use your dual batteries for welding, both 'Stick' and 'MIG' welding,
Take a battery out to use in camp, personally, I run fans and lights in my tent with my extra battery.

An 'Anderson' connector on the simple version lets you drop a battery out VERY EASILY,

I use mine to jump start the lawn mower,
Jump Start vehicles that are beyond the reach of my Jumper Cables,
Pull one battery for use in other vehicles I don't use very much (with Anderson connector installed),
Use the extra battery in my camp site, the 'Little Woman' likes having a fan, lights, cell phone charger, ect. in camp, and the extra battery works very well for those things.

Another version is Dual Battery with ISOLATION of the second battery.,


A single battery with Anderson connector makes for a safe (Can't be hooked up backwards on your end),
Solid Jumper Cable connection (no 'wobbling' jumper clamps for connection),
And it keeps the connection at your battery away from the explosive gasses!

But a second Anderson connector mounted on the front of the vehicle makes for a quicker connection and you don't have to raise the hood!


[B]If you have BOTH batteries on Anderson Connectors,
It's VERY EASY to adapt them for welding. All you need is three more Anderson connectors and some cable.

By disconnecting the batteries from the vehicle, and connecting them to a 'Yoke' that produces 24 volts, you can do simple stick welding, or if you have a spool gun, you can do MIG welding right off the batteries.

Since the batteries are disconnected from the vehicle, there is no worries about cooking your sensitive electronic components, alternator, MSD module, stereo are all safe since you have the batteries unhooked from the vehicle.

This arrangements also lets you weld with 'STRAIGHT' welding polarity (Work POSITIVE, Electrode NEGATIVE) which would kill your changing system and batteries if you tried it with batteries/alternator hooked up.[/B]


I use my jumper cables, since they are 4 AWG (American Wire Gauge) welding cable anyway, for the 'Ground' and 'Stinger' when 'Stick' welding.
This 'Yoke' makes for 24 volts output at around 200 Amps (restricted by cable size) and will do 'Rescue' welding quite well.

I use smaller diameter rods for 'Digging', Deep welds, and larger rods or reverse welding polarity (Work 'Negative' & 'Stinger' Positive) for lighter duty welding that doesn't require deep penetration.

· Premium Member
11,200 Posts
Discussion Starter · #5 ·
Battery information,
Connector Information,
Wire and Cable Information, ect.

Not finished yet, still working on diagrams, trying to get my crappy digital camera to work so I can take pics of Anderson connectors, jumper cables with welding adaptations, ect.

But this gives you guys some idea of how my rotted brain works me to death some times!



Batteries come in all Shapes, Sizes, Terminal Configurations and Types.

For the purpose of this article,
I'm sticking with Basic Type Automotive Batteries because they are the least expensive,
I'm sticking with Basic Type Automotive Batteries because they are the easiest to find,
I'm sticking with Basic Type Automotive Batteries because they are the most reliable 'Common' batteries,

Top Terminals because the larger top terminals have more contact surface area to transmit Amperage,
Top Terminals because they have the terminals above the electrolyte level, so they don't leak as much acid out where the terminals pass through the case,
Top Terminals because they are the LEAST LIKELY to get shorted out in a Jeep Application,

Lead/Liquid Electrolyte type because they are more reliable than 'Gel' cells or 'AGM' batteries (and MUCH less expensive!)

'Rough Service' or 'Industrial/Farm' use batteries because they are just plain built tougher...
(and I'm HARD on stuff! :D )

I also don't care for 'Maintenance Free' batteries because you can't service them, if they get low on electrolyte because of hard use (Discharging) or fast charging they loose moisture you can't replace.

"Rough Service", "Industrial" & "Farm Use" batteries also have Thicker Cases,
Heavier bridges between cells and posts,
'Caged' plates so the plates can't bounce out of the separators and short the cells out,
They have a 'Mud' tray at the bottom to catch debris off the plates so it doesn't short the cells out.

You can use what ever you want, but those are my recommendations.



Common 'Starting' Batteries convert the CHEMICAL ENERGY into Electrical Energy faster than DCM or "Deep Cycle/Marine" batteries do.

Deep cycle batteires are designed to discharge much further and recover when charged, but they do it SLOWLY.
When winching, you need A LOT of current very quickly and DCM batteries are often damaged by the process of draining them so rapidly.

Common Staring Batteries will convert Chemical Energy into Electrical Energy you can use much quicker, and in most cases, you WILL NOT discharge them so deeply you will harm them.
To me, it's not worth the extra expense of DCM batteries when Starting Batteries will do.

Gell Cell and AGM have two very fatal flaws for this application,

One is EXPENSE! They are STUPID EXPENSIVE and have little or no warranty.

The second is the gel electrolyte can't 'Off Gas' the hydrogen gass produced during rapid/deep discharging, so the bubbles of gas stay trapped against the plates, causing 'Dead' spots on the plates that will never transfer energy again.
This effect is cumulative, so the more you quickly Charge/Discharge, the more damage is done.


Connectors, Terminals, Miscellaneous.

Anderson Connector.

The Anderson Type connector has been an industry standard for many years because it WORKS!
It's common as nails, available everywhere from parts stores to E-bay,
And it moves large amperage loads.

I use them because they can't be hooked up backwards, They are sturdy and inexpensive, and they allow me to change out electrical appliances in seconds.

An Anderson Connector and Quick Release Battery in the world's Junkiest Jeep,


Several Vehicles used an oil pressure switch to activate the electric choke and/or the 'Idiot Light' on the dash.
These are VERY easy to find, cheap to buy and make for 'Automatic' safety switches for electric fuel pumps,

They are also very good at turning your electrical appliances 'On' and 'Off' with the engine without having to flip switches, like the above isolated battery systems, or things like electric fans, ect.

This particular one is from an '80s Chevy Truck...

If you shop around for different makers, different years, ect. you will find one, two and three terminal switches, long stems, short stems, 1/8", 1/4" threads, ect.



Relays come in an astounding number of shapes, sizes, Amp loads and do the switching when you don't want to handle the current loads yourself!

How A Relay Works, LINK:

The Smaller current circuit creates a magnetic field. That's all it does.
The magnetic field pulls in the larger contacts of the primary load device.

Switching is VERY quick, so you get less sparking/burning of terminal material,
And a very low current circuit can activate a much larger current load without having a bunch of current running all around the vehicle via wiring that might be pinched, burned, rubbed through, ect.


This is a rundown of small relays, most are 20/30 Amp relays, but some go up to 70 Amps without problems.
These are what is known as 'Continuous Duty' relays, which means they can be activated every minute your vehicle is running with no issues.
This will give you an idea of what is available, how to wire it and where to use it.

Larger Relays are often called 'Solenoids'. This is a misnomer.
A 'Relay' is an electromagnetic switch that uses small current to control a much larger current.
A 'Solenoid' is an electromagnet that works a mechanical device, like an air valve or hydraulic valve or moves a mechanical arm...



[B][SIZE=3]This is the 'Brown & Sharp' scale, the industry standard for over 100 years,
And this scale will tell you what size wire you need for any amp load device.

The sizes listed for Amp load rating are for CONTINUOUS DUTY use without the conductor (wire) heating up.
Since most battery/winch cables will NOT be used long enough to get them extremely hot, I Under-Sized a little bit rather than Over-Size wires like I do with things like Head Lights that will be used for hours on end.

If you take a close look at this scale, it would take a HUGE wire (or combined wires) to feed a winch drawing 500+ amps at 'Full Pull'...
Most of the time somewhere between 2 AWG and 2/0 Gauge wire will feed a winch just fine, but if you are in a long, hard pull, you WILL notice the cables heating up![/SIZE][/B]



Making Cables.

This is your basic battery/winch cable fabrication materials and tools.
Something Between 2 AWG (American Wire Gauge) and 2/0 (00 or 'Double Ought') Cable to start with,
Some Solid Copper, Lead Cadmium Plated Battery Terminals with Stainless Steel bolts and correct 'Terminal' nuts,
Some solid copper 'Lug' terminals,
Some 'Silver Bearing' Electrical Solder,
Some Heat Shrink Tubing with internal 'Glue' to seal up the connection,
Cable Cutter that will do double duty as a stripper,
And a Terminal Crimper.

Link to Image:

With this hardware, you can make about any battery cable you could imagine!

Start off with cutting to length, then stripping for terminal ends,

Link to image:

Give that sucker a good crimp for a MECHANICAL connection between cable and connector,

Link to image:


Link to image:

This shows SOLDER FLOWED into the Joint to make an Electrical Connection,
And the exposed wire was 'Tinned' so it doesn't corrode as easily over time...

Link to image:

Time for some HEAT SHRINK TUBING to reduce the amount of exposed conductor, and seal up the joint between cable and terminal.

Link to image:

Here is the HEAT SHRINK doing it's thing!

Notice the 'Glue' coming out of it?

That glue seals up the connection and keeps that cable from rotting out for a LONG TIME...
If you don't have 'Red' cable, A couple of inches of heat shrink can be used to label 'Positive' cables even when the wire insulation is 'Black'...

Link to image:

Strip, Insert, Crimp, SOLDER!, Heat Shrink...



· Registered
346 Posts
Another thread bookmarked in my "to do" folder. Funny that 95% of stuff I have saved in there from the internet is from JeepHammer...

Thanks for the write up! That seems like a lot of work, when do you find time to go Jeepin'?

· Premium Member
11,200 Posts
Discussion Starter · #7 ·
Trying to put all the relative information in one spot so it's not all over the place,
But I also have problems with 'Information Overload' sometimes...

Anyway, anyone have any suggestions on stuff I forgot to cover?

· Registered
1,754 Posts
Anyway, anyone have any suggestions on stuff I forgot to cover?
I found it very well written and detailed.

You may want to add something like whether the use of dual batteries warrants upgrades to the factory charging system, and what those upgrades may be.

Nice work JH, hopefully this will get pinned :thumbsup:

· Premium Member
11,200 Posts
Discussion Starter · #9 ·
One battery, two batteries, doesn't matter to the factory charging system...
It only 'Sees' one large battery when wired this way.

Now, if you have two different size or types of batteries (Starting with DCM) you need to do things a little differently because different sizes or types use different charge rates, but a 'Matched Set' of batteries will charge as one large battery, and your factory alternator is more than capable of doing the job.

The same Delco-Remy 10 SI alternator, or 12 SI alternator was installed on MANY vehicles with dual batteries from the factory, and it's amp capacity is more than enough to overcharge the batteries if it goes unregulated, so there aren't any issues with charging other than most of use 'Off Roaders' do our thing at low RPM...
And the 10 SI & 12 SI doesn't charge at low RPM very well...

But then again, the dual batteries will carry us through until we get the RPM back up, so it's a 'Win/Win' with dual batteries...

No alternator that would fit under your hood would keep up with a winch drawing 500 to 700 amps in 'Full Pull' trying to get out of a 'Bad Stuck' situation...
It would take a V-8 engine and generator nearly as large as the V-8 to make that much DC amperage directly!

It's AMAZING how much power a battery stores!

That's why a SECOND BATTERY is so important when you winch!
It's capable of keeping up with the winch for a short period,
Then the alternator takes over and recharges the battery SLOWLY like batteries like to be charged...

Second battery keep you from discharging the first battery too far so it's not damaged, and gives you more winch time.
With that second battery, you can do all sorts of other 'Tricky' things!
If it's there, why not use it for something other than occasional winching... ;)

Anyway, charging system upgrade is coming...
My alternator keeps getting packed full of mud, so an upgrade is coming when I pull this engine. Probably a CS series alternator, since they are cheap, available, simple to switch to, and work really well at lower RPMs.

The idea was to give EVERYONE something, from 'Simple' to extravagant with all the 'Whistles & Bells'...
Show the full range of what you can do with a second battery...
And how to make cables that won't starve your winch, connect the winch so it works 'Best', and to use what you have more efficiently.

· no balls
3,433 Posts
this is awesome, thanks jh, will be sure to use this when i can afford a second battery lol

· Registered
262 Posts
Just curious, I am setting up dual batteries in my CJ but I am using a voltage sensitive relay on mine and completely isolating the starter battery and using the other battery for all accessories. The VSR basically has both positive leads connected to it and switches from one to the other based on voltage. Once one battery is charged the relay pole gets thrown to the other battery for it to get charged so that it is charging them separately and the two batteries are never hooked to each other. Sorry this diagram is so "busy" I just use it as a reference for all of my wiring. I will break these out individually eventually but you can see the voltage sensitive relay as "VSR".

· Registered
262 Posts
Just wondering though if there's an issue keeping one battery only hooked up to the starting system and one hooked up to the accessories without having the two connected together. I want the system to stay redundent even if it's not benefiting from the higher amperage rating as your system due to the fact that in your system the batteries leach off of each other. In other words in your system if one battery fails they both fail. I want mine to stay reliable and I think that since mine is setup to have one battery starting and one battery powering accessories it should be plenty of power for everything. See any potential powers?

· Registered
717 Posts
What a great thread. Kudos to you! Bookmarked for future reference.

· Registered
37 Posts
I have recently bought a new "starting" battery and have a friend who has another good "starting" battery he is willing to give me. Will the fact that they have different CCA be a problem or the fact that one is brand new and the other is used but still testing ok?

· Registered
799 Posts
"Anyway, anyone have any suggestions on stuff I forgot to cover?" You were joking, right? Thank you Jeephammer for yet another overkill awesome write-up. Some of the stuff I have never even seen in pictures (batt. cables).

· Premium Member
11,200 Posts
Discussion Starter · #18 ·
From the starter relay to the starter, you can use what ever you want,

But the 'GROUND' or NEGATIVE to the winch needs to be as large as the input to the winch,
Most people screw that up and don't provide a solid 'Ground' for the winch...

BATTERY POSITIVE TO WINCH needs to be as large as you can find, 2 Ga. MINIMUM to supply a large winch properly.

· Registered
1,082 Posts
From the starter relay to the starter, you can use what ever you want,

But the 'GROUND' or NEGATIVE to the winch needs to be as large as the input to the winch,
Most people screw that up and don't provide a solid 'Ground' for the winch...

BATTERY POSITIVE TO WINCH needs to be as large as you can find, 2 Ga. MINIMUM to supply a large winch properly.
I'm using 00 welding cable for the positive and negative.

· Premium Member
11,200 Posts
Discussion Starter · #20 ·
Can't go wrong with that!
Anything above about 2/0 Cable and you are reaching the point of diminishing returns.

I've tried larger cables, and the motor still heats up as much as it did with 2/0 cables,
In fact, 2/0 is a bit big, but I want my winch to get everything it can use even when the cables/terminals get older and have slight problems with corrosion and such.

So I'd say the motor terminals can't handle any more delivery, and there isn't anything you can do about the (usually) steel terminals in the winch motors without owning your own electrical shop and doing WAY MORE work than is needed...

Keeping rust/corrosion off those motor terminals is a FULL TIME JOB!
We wheel a lot in old coal mine pits, and the water there is corrosive like crazy!
(The only thing I've found that is worse is salt water!)

I'm big on keeping those terminals well protected, dielectric grease or battery terminal protector spray is your friend in those cases!
The more water/corrosives/oxygen you can seal out the better!
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