# Adding 2nd Battery to Truck - Auxiliary Battery Isolator



## Sean H

Just got a new to me slide in dog box with fan, water pump, and airing light. 

Did quite a bit of research to figure out the best way to hook it up to my truck for both longest fan run time and without having to worry about not being able to start the truck due to a dead battery, and wanted to share what I found.

The first thing I thought about was whether to get a 2nd battery for the box, or just get one of the battery brains that keeps you from draining your battery below the cranking voltage. I decided on a 2nd battery because the stock truck battery is not designed for deep cycle use, and therefore wouldn't provide as much run time and would eventually fail prematurely due to the constant deep cycles.

So now, what's the best way to hook up the deep cycle battery to your truck so that it charges from the alternator but is isolated from your cranking battery? There's many ways to skin a cat, and this is much the same. Many ways were cheaper than the route I decided on, but much more complicated or not quite the assurance I was looking for.

In the end I decided on this isolator (http://www.hellroaring.com/bic75150.php). Very easy installation with one wire to each battery (with circuit breaker in line) and one ground wire. This setup keeps the batteries isolated until the alternator starts providing a charge.

Also, for those of you with Chevy trucks, I found out that there is a stock 2nd battery tray for the engine compartment. Just go to the parts department and ask for it and you'll have 2 batteries under the hood and not have to worry about someone stealing it out of your bed or having to put it in the cab.

I'll post pics up once I get it all installed.


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## Jim Scarborough

Great post. Can't wait for the pictures. Thanks.


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## Sean H

Check back next week for pics guys. Just got the shipping info and I'm not going to recieve the isolator until next Monday.


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## jeff t.

Sean H said:


> Just got a new to me slide in dog box with fan, water pump, and airing light.
> 
> Did quite a bit of research to figure out the best way to hook it up to my truck for both longest fan run time and without having to worry about not being able to start the truck due to a dead battery, and wanted to share what I found.
> 
> The first thing I thought about was whether to get a 2nd battery for the box, or just get one of the battery brains that keeps you from draining your battery below the cranking voltage. I decided on a 2nd battery because the stock truck battery is not designed for deep cycle use, and therefore wouldn't provide as much run time and would eventually fail prematurely due to the constant deep cycles.
> 
> So now, what's the best way to hook up the deep cycle battery to your truck so that it charges from the alternator but is isolated from your cranking battery? There's many ways to skin a cat, and this is much the same. Many ways were cheaper than the route I decided on, but much more complicated or not quite the assurance I was looking for.
> 
> In the end I decided on this isolator (http://www.hellroaring.com/bic75150.php). Very easy installation with one wire to each battery (with circuit breaker in line) and one ground wire. This setup keeps the batteries isolated until the alternator starts providing a charge.
> 
> Also, for those of you with Chevy trucks, I found out that there is a stock 2nd battery tray for the engine compartment. Just go to the parts department and ask for it and you'll have 2 batteries under the hood and not have to worry about someone stealing it out of your bed or having to put it in the cab.
> 
> I'll post pics up once I get it all installed.


Could the isolater be plugged into a powerpoint inside the vehicle? I have a couple of crate fans I want to run off of deep cycle battery, and would like for that battery to be charged by plugging into a powerpoint located near the crates.


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## Sean H

jeff t. said:


> Could the isolater be plugged into a powerpoint inside the vehicle? I have a couple of crate fans I want to run off of deep cycle battery, and would like for that battery to be charged by plugging into a powerpoint located near the crates.



I'm guessing you don't want the battery hard wired so that you can take it out? What kind of powerpoint are you talking about?


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## Jay Dufour

I had the isolator installed at NAPA Auto Parts for 160.00.It charges my battery for fans ect.,but will never deplete my truck cranking battery.Its been in service for 9 years.Oh.They have a chip in them that wont overcharge the battery also.


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## John Lash

I plan on getting the extra battery too.

I've looked at deep cycle batteries, expensive... How big of a battery does one need for a water pump and a fan?

John Lash


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## jeff t.

Sean H said:


> I'm guessing you don't want the battery hard wired so that you can take it out? What kind of powerpoint are you talking about?


Similar to a cigarette lighter outlet. The fans are in the interior of a Ford Econoline van.


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## Sean H

John Lash said:


> I plan on getting the extra battery too.
> 
> I've looked at deep cycle batteries, expensive... How big of a battery does one need for a water pump and a fan?
> 
> John Lash


It depends on how long you want to be able to run the fan, and what physical space you have for the deep cycle battery. Marine deep cycle batteries are larger physically, but cheaper and comperable in performance to the high dollar deep cycle batteries. In my case, I didn't have a spot for a big marine battery and wanted to be able to run my fan all day, so I opted for a high dollar Odyssey dry cell battery.




jeff t. said:


> Similar to a cigarette lighter outlet. The fans are in the interior of a Ford Econoline van.


The thing I would be concerned with here is the guage equivalent of the cigarette lighter and the wires that come attached to it. There's a lot of amps (~60 on a stock alternator) running between the alternator and the battery and you need 8 guage wire between the two.

Another concern might be the potential to get electrocuted pretty bad if the battery wasn't installed in the cigarette lighter. That wouldn't be your normal lighter that would be limited around 20a, it would have a lot of juice running to it.

Thinking about it, you'd probably be better off finding a high current electrical outlet (maybe clothes dryer outlet) for home use and using that with a normal power cord.

I would call the guys up at Hellroaring and ask them about it. They were very helpful when I spoke with them.


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## Sean H

Sorry for the delay guys, kept forgetting to take a picture.

Here's the engine compartment of my truck. You can see the 2nd battery in the top left. Right next to it is the battery isolator. There are three wires coming off the isolator, one to the 2nd battery, one to ground, and the third to the alternator (could have been hooked to the original battery, but in my case it was easier to hook to the alternator).


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## Jay Dufour

Hi.Just a heads up.....The isolator system I had installed on my two month old Tundra fried my alternator Saturday.I ran the fans all night Friday at the motel,and it ran down the extra battery.When I started the truck to go out to the hunt test,it must have been asking for too much power....dont know but I was running off the main battery which put me on the side of the road.I had to wait till Monday to get it to a dealership.They were nice enough to warranty the alternator,but advised me not to hook the isolator back up.....because next time its on me.Going back to 115v off the generator.


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## Vertigo

That is why I opted away from the isolator. Also, when using an isolator, the alternator does not see the voltage drop on the second battery and kick into high output charge. I chose to use a high amperage, continuous duty relay, switched off of the ignition. This totally removes the second battery from the system when the truck is off, not touching the running battery. When you turn the key on, start the truck right up, and the second battery is connected to the system and is quickly charging. I can run my topper fans all day off of my deep cycle and not have any issues starting the truck.


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## Paul Fix

I looked into an isolator installation for my truck to run my 3 speed crate fan but decided to go a different route. I purchased an AGM style battery that cannot spill acid on the dog. I secure the battery in the bed of the truck with a bungee cord. These batteries are most commonly used in wheelchairs. I also bought a wiring adapter kit that allows me to hook up to the battery and it has a cigar lighter socket to plug the fan connection in to.

The battery is small and light with a carry handle that makes it easy to carry back in the house to recharge when I have finished using it. I can get 12 hours plus of run time on high speed. I was very concerned about the acid spill hazard from a marine style deep cycle battery. With the AGM style batteries you do not have this worry. It is much safer for the dog. I purchased my battery from Batteries Plus for about $80.


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## Jay Dufour

I'm gonna go with my honda 2000I to keep the 12V system charged,and also run some 115V bigger fans while at trials.It has a 12V charger port and wire to do this. They say the new trucks are so sensitive that any spike or oddball incident can cause the system to go down.


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## Sean H

Jay, the system I put in allows you to put in a much larger alternator, up to 300 amps I believe. Might want to check into that.


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## dnf777

Jay Dufour said:


> I'm gonna go with my honda 2000I to keep the 12V system charged,and also run some 115V bigger fans while at trials.It has a 12V charger port and wire to do this. They say the new trucks are so sensitive that any spike or oddball incident can cause the system to go down.


How bout one of those bicycle generators that you'd flip down onto the rear wheel to power the headlight? :-x

I'm just now adding a cap and drawers to my truck, and am afraid to tie into the electrical system at all, given my experience with tripping computer chips!


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## Jay Dufour

Dig this.....They ASSSUMED that the alternator was fried when they saw the isolator,so the replaced it.It didnt work....they checked a fuse ....it was broke.Soooooo they charged Toyota for a replaced alternator ......when they could have checked the fuse first,and saved seven hundred.The fiasco caused me an extra night in motel 88.90,two days lost work,three round trips 178.3 miles one way on two trucks.Also I got home and the engine splash shield was in the back of the truck with no bolts to put it back on.....They FORGOT to put it back on.Now I have to depend on them to mail me the bolts and directions to replace it ! WWWWWWTTTTTTFFFFFFF


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## Rich Schultheis

any updates on how these systems work? Deciding which way I want to go with my truck.


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## Troy Tilleraas

I have a unit been working for over 2 years. FWIW I am a master electrician and work on elevator controls, Use a 100 amp isolator with builtin relay for cutting out the vehicles battery, 6 gauge wire from the vehicle battery + to isolator (in side) out side to + dry cell battery I used a Werker 1200 amp unit from Batteries plus. Parallel from the battery to your 12 v lights fan etc install an inline fuse and use 12 gauge wire for the + side. Also parallel of of your battery to a 1000 watt converter. 6 gauge wire from the frame of the vehicle to a grounding position in your box etc and parallel off of that to you box battery. Make sure your grounds are in location and a secure tie point if a stainless or aluminum box! I'm assuming your isolators cut out switch failed and drained your electrical system.


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## TN_LAB

pondhopper said:


> any updates on how these systems work? Deciding which way I want to go with my truck.


What are you going to be powering?


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## labluver

I thought I wanted an isolator when I put my 2nd battery in but a call to this placee convinced me otherwise. I have a 2007 Chevy Silverado with a 3 hole box, airing lights, fan, 1200watt converter, water pump, storage lights, charging rack.. blah blah blah. I was told what I needed was a battery separator. Well I put in a separator and have had no problems. Always have a fully charged battery for starting. Check out this website. It explains the system and says it protects your charging system. I have actually had it to work. Left some stuff on in my box for a few days and ran the battery that supplies box power completely down. Truck started right up with full battery, then it charged my box battery. I can say that it works great. I installed it myself. Only challenge was getting the dash covers off to find wire at steering column. You can buy all the cables at a local auto supply already made up. 
http://www.ase-supply.com/Sure_Power_Battery_Separator_s/154.htm


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## Jay Dufour

That is what I ended up with....used in tandem with a onboard charger for "shorepower "during the summer.Also from surepower.


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## Georgia.Belle

I have had the hellroaring for about a year, no problems.


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## Rich Schultheis

going to be running three fans, don't want to have to worry about if truck will start or not. new truck came with second battery tray already in there, so going to try something or another.


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## TN_LAB

pondhopper said:


> going to be running three fans, don't want to have to worry about if truck will start or not. new truck came with second battery tray already in there, so going to try something or another.


Others have given good advice on making it look and run like a factory installed/stock setup. Of course, that route is a little more expensive.

Cheap route would be to get a rechargeable battery and keep it charged. Deep cycle and/or marine batteries are nice, but might be overkill. A simple deer-feeder battery might give you enough run time between charges.


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## Rich Schultheis

goin with a relay setup using second battery tray under the hood and alt to charge. Have used a deep cycle in the back i would take out and charge in last truck, it was a pita. thanks for all the advice folks let you know how it works when its done


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## Jason Glavich

some small solar panels and a deep cycle battery would work for this also. Panels are getting cheaper and as long as you stick with small ones on top the box or removable they would work great. I know a guy who uses 2 medium size ones for his camping trailer, runs everything except a microwave(fridge is LP). He said he did it to get away from the generator noise. But I am sure you could run some fans with a deep cycle and panels.


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## Tom D

I have been sing isolators for over twenty years on both my boats and trucks. 

Only had a problem once on my last truck. Seems somebody pulled a fast one on the Pep boys where I purchased it. You have to match isolator with alternator amp out put.

I had a 125 amp alternator at the time. The box had 125 amp marked on it. After it was installed the isolator and I used the secondary battery it fried some wires and isolator. What had happen was that the box actually contained a 90 amp.

You can always go larger, don’t cut corners.


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