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Radio Equipment Installation Forum - Forum for discussing how to install radio communications equipment in Mobile, Base, Command Post, EOC, etc configurations.

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Old 11-08-2017, 9:51 AM
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Default Backup battery Installation

I would like to install a backup battery in a vehicle so that I can run the radios and other equipment of of one battery constantly and not drain the main battery. I have looked around at the forums but not found much help as to how I can do this. If someone can explain how I can wire this up I would appreciate it.

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Old 11-08-2017, 10:08 AM
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You'll need wiring, charging capability, voltage regulation, etc. plus a place to put the new battery. In newer vehicles, the engine compartments are already full. It would be a major undertaking as an add-on.
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Old 11-08-2017, 10:09 AM
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Originally Posted by kd8nxh View Post
I would like to install a backup battery in a vehicle so that I can run the radios and other equipment of of one battery constantly and not drain the main battery. I have looked around at the forums but not found much help as to how I can do this. If someone can explain how I can wire this up I would appreciate it.

73,
Augustine

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What your looking for is called a battery isolator. It allows the charging system to keep both batteries charged but isolates the two batteries from each other while in use. This allows you to connect your radio to the secondary battery and prevent your primary, starting battery from discharging while using your radio. Isolators are quite common in RV vehicles and trailers. Below is a link to one I found quickly on Amazon. I have no experience with it whatsoever so please don't think I'm endorsing it. I was just using it as an example. I hope this helps.


https://www.amazon.com/Cole-Hersee-4...ttery+isolator
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Old 11-08-2017, 10:21 AM
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I take it constantly means with the engine shut off, correct? If your car is running you won't drain your main battery. Article about car audio which contains good info.:

https://www.lifewire.com/second-car-...e-audio-534761

"Whether you install a high capacity battery, or a second battery wired in parallel, itís important to remember that youíll only really see a benefit when the engine is off. Thatís when the extra capacity really comes in handy. Whenever the engine is running, the extra battery is just an extra load as far as the alternator is concerned, which can overstress an old (or underpowered) unit."
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Old 11-08-2017, 10:31 AM
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Originally Posted by bb911 View Post
I take it constantly means with the engine shut off, correct? If your car is running you won't drain your main battery. Article about car audio which contains good info.:

https://www.lifewire.com/second-car-...e-audio-534761

"Whether you install a high capacity battery, or a second battery wired in parallel, itís important to remember that youíll only really see a benefit when the engine is off. Thatís when the extra capacity really comes in handy. Whenever the engine is running, the extra battery is just an extra load as far as the alternator is concerned, which can overstress an old (or underpowered) unit."
Yes that is correct.

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Old 11-08-2017, 10:33 AM
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I ran a battery isolator in my truck for many years back when i was active with volunteer fire dept.
Other then burning out my factory alternator and needing to replace it with a higher capacity one it was a good investment.
If your running a few radios you should not have to worry about the alternator. I had radios and lights on my truck so having lights put extra load on the alternator.
If you dont have room in your engine compartment you can run a main power line from the isolator to the trunk if in a car or bed if a truck (make sure battery is in a weather proof housing).Then run power from that second battery to the radios.
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Old 11-08-2017, 10:46 AM
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Quote:
Originally Posted by kd8nxh View Post
I would like to install a backup battery in a vehicle so that I can run the radios and other equipment of of one battery constantly and not drain the main battery. I have looked around at the forums but not found much help as to how I can do this. If someone can explain how I can wire this up I would appreciate it.

73,
Augustine

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How to make a cheap isolated dual-battery setup for $50
How to make a cheap isolated dual-battery setup for $50 - Expedition Portal


Details about Speed G1200A Battery Relocation Kit Trunk Mount Battery Kit w/Cables
https://www.ebay.com/itm/Speed-G1200...-/191077325861
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Old 11-13-2017, 3:07 PM
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Quote:
Originally Posted by iMONITOR View Post
How to make a cheap isolated dual-battery setup for $50
How to make a cheap isolated dual-battery setup for $50 - Expedition Portal


Details about Speed G1200A Battery Relocation Kit Trunk Mount Battery Kit w/Cables
https://www.ebay.com/itm/Speed-G1200...-/191077325861
I don't support this type of connection due to the fact that you could blow up a battery if the second battery was almost dead and you activated the relay. It would cause a massive inrush of current from the charged battery and could cause serious damage if a plate shorted out.

The use of a dual battery isolator is the safest way to go. Any time the engine is running, it will keep both batteries charged. When you shut off the engine, only the second battery will be used to run your aux equipment connected to it.

I also ran one of these in a service van I had for many years. Never had to worry about killing the main battery to start the engine with.

As has been already pointed out, you may want to consider upgrading your alternator to be able to handle the extra load in trying to charge the second battery if you suck it down very much. A normal vehicle alternator is sized to handle the normal vehicle load, hat the vehicle has. If you add much above the normal load it was designed for, you could run into problems down the road.

An example of this is like in my Ford F250 diesel I have. I took out the alternator twice. Then I up sized the alternator. So far I have not had a problem since. The last time I changed it, it only took me 15 minutes. I have had the truck since 2004 and put a number of miles on it.

When you do go to add the diode isolator, you will need to move the connection from the output of the alternator and tie it to one side of the diode isolator. Then run a new wire from the alternator to the common of the diode isolator. The second battery goes to the other side of the diode isolator. Don't forget that these wires need to be sized to handle the charging current going to the batteries. The wire going to the common point of the diode isolator needs to be sized to handle the full rating of the alternator output.

Hope this helps. It may sound like a bunch of effort, but if you use your vehicle out in the boonies at all with the engine shut off, you will come to a fast conclusion that the diode isolator will pay for itself the first time you find you have killed the normal vehicle battery playing with your radios with the engine shut off.

One other thing that I did was to add a starter solenoid with a push button under the dash. This was used to connect the 2 batteries together in an emergency if the vehicle battery won't let you start the vehicle. I have got caught a couple of times from leaving a door open and drained the vehicle battery way down. it wouldn't start the vehicle. Pressed the emergency button and was able to start the vehicle. just make sure your power source for the button comes from your second battery.
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Old 11-13-2017, 4:53 PM
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And some of us have vehicles with no available space in the engine compartment, no trunk and not a chance of putting it anywhere else.
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Old 11-13-2017, 10:14 PM
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And some of us have vehicles with no available space in the engine compartment, no trunk and not a chance of putting it anywhere else.
The Chevy Silverado 1500s have a second battery tray in all of them by default.
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Old 11-13-2017, 10:48 PM
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The Chevy Silverado 1500s have a second battery tray in all of them by default.
Kia was not that thoughtful when they created the Sorento.
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