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Dual battery and fridge install write up

17K views 33 replies 13 participants last post by  RenegadePirate 
#1 ·
Recently installed a dual battery system and fridge for my Frontier to make camping, road tripping, and ‘overlanding’ a little bit easier with the family. Just wanted to share the install details and information I have discovered so far.

I used a “TrueAm Smart Battery Isolator” that I purchased for about $80 dollars on Amazon. It is a voltage sensing relay (not like the old diode style isolators) that opens the connection between the two batteries when the starter battery reaches 13.4 volts and then disconnects them when the starting battery drops below 12.9 volts. SO basically it allows a connection when the car is running, disconnects when the car is off. Very simple setup. Does not have a manual on/off switch, or disconnect switch, or jumping capabilities, but I did install Anderson plugs between the two batteries so that I could just disconnect and remove the auxiliary battery when I wasn’t using it.

I used 4awg wire and ran it from the starter battery to a mega fuse 100amp fuse, then to the isolator (you want to mount the isolator as close to the battery as possible) and from the isolator through the firewall gasket behind the glove compartment. I then ran the cables behind the plastic trim and out underneath the passenger seat. Those cables end in Anderson plug. My battery box then has another 100amp mega fuse in it so that there are fuses on each side. Battery is a 100amp hour AGM battery since it is inside the cab. Fridge is a Dometic CFX35, their new line that only draws about 0.5 amps per hour from both my testing and others. The fridge is mounted to a Dometic fridge slide which is bolted to wood that is strapped to the seat.
 

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#2 ·
I have measured my voltage and amp draw and my starting battery always reads between 13.8-14.2 like clockwork across the posts, and the auxiliary reads just about the exact same amount except for about a 0.1 voltage drop across the roughly 10ft of cable. If the battery is at around 50-60% charge it draws up to 40-50 amps initially and then after about 20-30 minutes is down to around 5-10 amps of draw. If the battery is fully charged it does not draw any amps. Thus far everything works perfectly and the alternator seems capable of recharging the auxiliary battery to about 80-90% in about an hour or two, tops, and then slows down and will take a few more hours to charge to 100%.

With my 100 amp hour battery I am able to easily get 2-3 days running the fridge with normal use without dropping below 50% (without charging it at all). Fridge draws a max of 3.5 amps that I have observed when it is on and cooling, but as I stated earlier once cooled only averages about 0.5 amps per hour.

Let me know if you have any questions, hope it helps ya'll out!
 

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#3 ·
My battery box is a Minnkota trolling motor battery box that has built in cigarette plugs and built in breakers, LED charge status, external battery posts, and pretty heavy duty handles and straps. Works awesome. I cut two holes it so that I could snake out some heavy duty cabling and also the cabling the fridge connects to (the fridge comes with a cigarette plug style DC plug, but I switched it to Anderson plugs).
 
#5 ·
What is your family size. Surprised it is not in the bed under a camper.
Family of three. Car seat is on the other side. Trust me, I wanted to put it under a camper shell, but I asked the wife and she said; "I don't want one of those, I want your truck to look like a truck". Literally word for word. With the pull out slider though it makes it really convenient for the family during road trips and having the fridge in the cab is nice so that my wife can pull out stuff like milk, juice, snacks exc for our little girl.

Tell the truth: you really like COLD road sodas!!
Also true.

2-3 days on one battery. That is better than I thought for a compressor type fridge.
How long you get on one charge depends totally on fridge and battery size. 100 amp hour battery is pretty good size, and the fridge is literally the most efficient fridge on the market currently, beats a comparably sized ARB (both made by Dometic) by about 70%.

Installing the fridge in the bed with a camper shell on it would have been way easier, both in regards to bolting the fridge slide down, and running wire. Could have just dropped the wire along the chassis and then drilled out a hole in the bed and made your own grommet. Running 4 awg wire through the firewall was a PIA.
 
#7 ·
Thanks for the write up, I'm planning on adding a second battery as well. Any thoughts of removing the rear right side seat for more space?

Sent from my SAMSUNG-SM-G920A using Tapatalk
 
#9 ·
I added one under the hood where the air filter was. Just used a high amp
relay to isolate it from the start battery when the ignition is off and
100 amp circuit breaker. 1/0 gauge (low resistance) goes along the frame
and enters the cab through the rear vent.

So far it's been working great, I did trip the breaker once while blowing
insulation into an attic at a construction site, I'll eventually upgreade
it to 120 amp (it's 80 amp now).
 

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#31 ·
I added one under the hood where the air filter was. Just used a high amp
relay to isolate it from the start battery when the ignition is off and
100 amp circuit breaker. 1/0 gauge (low resistance) goes along the frame
and enters the cab through the rear vent.

So far it's been working great, I did trip the breaker once while blowing
insulation into an attic at a construction site, I'll eventually upgreade
it to 120 amp (it's 80 amp now).
I love that setup where the rear seat used to be. It's exactly what I've been thinking of building for my overland rig.
 
#10 ·
I've been reviewing the installation of my second battery and got to wondering about the "variable voltage control system"
and how the presence of the current sensor (pictured below) effects the charge of the second battery.

Anyone have thoughts on how the grounding should be done to make sure the second battery is accounted for in the
alternators charge rate?

Right now I have the second battery grounded the the body frame since everything it's powering is also grounded to the
body or frame. I'm wondering if I need to run the second battery's ground directly to the primary battery's ground in
order for the current sensor to detect the drain on the second battery and increase the charge rate.

If so, of course I'd have to have a larger gauge cable going through the current sensor to carry the load of both
batteries.

Anyone dealt with this? This is the first time I've had the VVCS on a vehicle so it's new to me.
 

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#14 ·
No, nothing I can tell. The engine runs strong, no codes, can still make the 300 mile trip up to
Georgia to visit the grand kids on a single tank. Took it to the dealership to get serviced ( don't
usually let anyone else work on my truck, but 2yr. free service ) and they didn't freak out about
it or anything. lol

I looked at some aftermarket intakes, but even though I could afford one since I'd set aside some
money to mod the truck when I got it, I just couldn't convince myself they were anything but very
expensive plastic tubes. There's a fine line between indulging yourself and just throwing your
money away ::wink::, and I'd have had to mod that anyway to fit in the space available.
 
#20 ·
This is amazing and very helpful! I'm just about to start a very similar project but mount the battery in the truck bed. I may run an accessory wire from the bed (through brake light above the bed) into the back seats so i have the option of both fridge mounting options.... if i can find a good way to seal it.

one question, what did you do with ground from the aux battery? frame, starter battery neutral or onto the engine ground?
 
#21 ·
Just a general word of wisdom, you do not ever want use a neutral as a ground ever. It is meant to be there as a back up only, and combining the two creates a potential hazard for electric shock, should anything short out. That being said using a clean bare metal portion of the frame is not a bad idea, especially considering the wiring to go back to the engine ground would be a more complicated and unnecessary process.
 
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#22 ·
Martinogg2: I am working on my second battery setup and I bought two 4 gauge wires and ran them from the battery, alongside the frame into the front of the bed. I build a board where I installed my DC to DC charger and a switch panel. I bought negative ground insulated battery junction Post block M8 Studs and connected the ground wire from DC to DC charger and from the primary battery and secondary battery to it. These M8 studs are available on Amazon. I plan on installing a fridge in the bed on a slider. Hope this helps
328114
 
#23 ·
The aux. battery will be located to the right side of this board. Another 4 gauge wire will run from the DC charger to the battery. I will run it from behind this board to the battery. A 6 awg wire will be connecting the aux. battery to the switch panel. there is a hole in the back of the box where the positive will be entering the switch panel. The Renogy DC to DC charger has MPPT built into it o a future solar panel can be installed on the roof of my truck feeding the energy to the DC charger. All of the switches have a fuse in them. I brought the positive and negative from the primary battery in the bed through the drain on the front of the bed. It is located behind the board and the plastic cap can be popped out. I drilled a hole in that cap and installed a rubber grommet through which I ran the wires. I am working on the slider and the next purchase would be fridge and battery. Not yet decided to go with an expensive fridge or a cheap one.
 
#24 ·
That helps alot thanks again, nice setup! Ive heard those DC to DC chargers are even better than the smart chargers. Ive just ran my wires from the starter battery into the truck bed today with 4 gauge wire and started building up my battery box so making steady progress. Yeah i brought them through the rubber grommet at the back right of the bed too, next big step is getting two 10 gauge wires into the cab back seats to run the fridge. thinking through the 3rd light brake light, ive ordered some gland grommets. i dont have a canopy (just bed bars and a RTT) so would like the option of mounting the fridge in both locations
 
#27 ·
4GA should be fused at a max of 100a for safety. 120a would be possible and should not present a fire hazard, but is not recommended for continuous duty.
 
#29 ·
Fridge should be fused independently, fused branch line sized and protected according to the measured draw of the branch equipment, just like homes have a central breaker at 200a, etc, and then branches at 15, 20 or 30a each. The main 100 or 120a is to protect the line / circuit running to the cab, truck bed, etc from catching fire if it rubs through and shorts to chassis ground.
 
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#32 · (Edited)
Renegade: I thought about that setup initially. My thought was to even shorten the distance from the starter battery but then I decided against it. I could store more valuables in the King Cab than the battery, so I went this route. I have been busy with work and have not done much to the truck. Saw some AGM batteries (of all the places) at an outdoor store. But have not purchased it.

Oh and I designed a countertop out of a 54 inch by 17 inch Yellow Pine for the truck tailgate. I used one of the scree holes on the left side of the tailgate so that I can rotate the countertop 90 degrees when open. Purchased a NutRivit gun and rivet some additional holes to stabilize the countertop when open or locked. Then used a 17x17 inch leftover piece of the same pine and connected it with Pino inch to the Pine countertop to make it a foldable sink. The countertop is locked with two bolts on the tailgate and in open form, the same bolt is used to secure it. the other end is supported by a modified tent pole. I think it came out nice. Pictures coming soon.
 
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