Dual Batteries installation.

[SnowDrifter]

So it's said: Whether or not you want to use an isolator is going to be hugely dependent on your setup.

If you want some extra starting power in cold weather, don't use an isolator. It's just another part to fail

If, however, you're in a scenario where you need to run tools / audio equipment / lights / etc with the car OFF, then it would make sense to use an isolator


There are 2 types:
1. Relay based
- More efficient
- More wiring involved
- Prone can be prone to failure
- Can be prone to a backfeed scenario where, if your alternator is struggling to provide appropriate output to charge a dead secondary battery, the charged battery will transfer charge across the voltage different. Err on the side of larger cables than smaller ones
- Smaller, more mounting options

2. Diode based
- Less efficient. A diode will cause a 0.7v drop and will dissipate heat according to 0.7*I, where I is the supply amperage from your alternator
- Easier to wire. No triggers. They're passive
- Prevents a backfeed scenario
- Larger, need to consider cooling

 

[jsoltren]

I've done some power electronics design in a past life and might think about building my own isolator.

What I really want is to make the secondary battery a deep discharge battery for running devices such as an inverter. I'd run the batteries in one of these modes:

Charging (alternator turning). 12V power tops off both batteries, but they are not connected to one another.
Isolation (engine off). Deep discharge is disconnected from the rest of the vehicle but can still run an inverter.
Accessory (engine off). Deep discharge can power 12V accessories instead of starting battery, but is disconnected when high current drain is detected if trying to start.
Emergency. Both batteries are connected directly in parallel for 30 seconds, in order to jump the vehicle if the primary start battery is dead.

I'd also like to add a roof mounted solar cell array for running tools and maintaining the deep discharge.

 

[jsoltren]

> If I end up keeping my GMT800 Denali I may look into a dual battery mod for it.

It's even easier on the GMT900.

 

[jz57]

The factory dual battery with an isolator set up is NOT ideal either, when the engine is cranking, both primary and secondary batteries are connected in parallel, if one of the battery is weak or undercharged, the other battery has to provide charging to weak one and cranking the engine in the same time.
The following setup is considered as ideal:

1) Ignition key in "Lock", "Access" or "Run" position when the engine is not running:

Primary battery is connected and provides all power supply, and secondary battery is disconnected.

2) Ignition key in "Cranking" position:

Primary battery is disconnected, and secondary battery supplies power.

3) Ignition key in "Run" position and the engine is running:

Both Primary and secondary batteries are connected and being recharged.

At Step 2 and Step 3, the wire connection is difficult without electronics circuit.

 

[BG1988]

For the last 6 months since I bought this truck, I have been using the empty second battery location for food runs transporting Jack in the Box etc so it stays hot and doesnt smell up the rig.
Gonna lose that when my battery dies and I replace with 2 new ones and cables......waiting for battery to die......

uber eats?

 

[Raptor Tahoe]

I waited till my old battery started to fail so I could install a second battery.. I have heard pros and cons about using electronic dual battery kits that are very expensive and I have seen a lot of vehicles with dual batteries hooked up in a parallel configuration with out those kits. There are a lot of factory vehicles that do not use the kit or any isolation kits. I have done this with several chevys in the past that went well over 250,000 miles with no problems and I installed this one 3 weeks ago.

Set up is very easy on the front right side looking under the hood there is a battery tray the factory installed but never used.

Parts list

• Battery hold down and bolt. You can get them from an auto parts store or the dealership it is the same part used for your existing battery
• Two new batteries. It is best if you replace both batteries at the same time.
• 36 inch negative battery cable.

• 65 foot positive cable.

1. Installation is pretty easy replace the old battery but do not attach the cables yet.
2. Install the second battery in the front battery tray and bolt it in.
3. If you have any large draw items like a winch or big stereo system you should attach it to the second battery.
4. Attach the 6 foot positive cable to the original battery block be sure to attach it to the battery side of the fuse block.
5. Attach the other end of the cable to your second battery you can run it along the fire wall or across the top of the motor.
6. Attach the negative cable to an empty bolt hole on the cylinder head
7. Both positive cables should be connected now if you didn't already so, it is time to attach both negative battery cables to their respective battery posts.
8. Re check all connections to be sure they are tight and you are ready to go.

In the future I may install a cut out switch that will cut the power from the main battery when I run my winch or decide to run a stereo and lights when camping so the other battery will be unaffected.
View attachment 193818

Nice job! Totally agree on the benefits of two batteries. Plus, the space for the battery is already there. After reading a million ways of doing the install, I went with a Keyline isolator and have zero problems for over a year. The kit came with everything I needed for wiring. Just added batteries and a tray with strap.

this is the kit...

 

[rzabel]

I had a dual battery system installed with an isolator. I did it because I had to leave my truck parked for weeks at a time and I had electrical gremlins that would drain my battery sometimes, but not all the time and I couldn't find the problem. I also use an electric cooler and other camping accessories. The system worked, but: 1. As noted, if one battery is dead, the second battery is charging it and starting at the same time. I experienced that, and it still started the truck - but just barely. 2. It is possible to completely discharge the primary battery to the point that there isn't enough power to close the isolator and use the second battery. Twice I had to jump the isolator so I could start the truck with the second battery. I have since installed a dash switch to use the second battery to open the isolator. However, after all this, I went through and pulled a mile of wires and a couple aftermarket items from the truck (principle problem was an old remote start), and I haven't drained the battery since.

 

[Tozan]

I run a refrigerator 24/7 in mine.

 

[Tonyrodz]

I run a refrigerator 24/7 in mine.

That's cool. Where do you have it?

 

[Tozan]

That's cool. Where do you have it?

I have it installed right behind the front passenger seat. I removed the mid-seat.

Here are some tips for a fridge...
In the summer for cold water I run it 24/7 at 45 degrees.
If I do a shopping trip in town (80 miles away) I will turn it down to 32 degrees.
I pre-cool my water bottles in a spare fridge in the garage.
I also put about 10 bottles in there to keep it cooler and reduce how often the refrigerator motor runs.