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Why two batteries

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Old Dec 4, 2012 | 11:54 AM
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Why two batteries
Still learning about diesels and need to know why the truck has two batteries

Is it to crank engine over?

Overall power needs?

Also is one a primary and the other secondary?

Thanks
 
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Old Dec 4, 2012 | 12:04 PM
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It's a big motor with high compression and it takes a lot of power to turn it over to start it. Even the 5.2 four cylinder Isuzu oil burner I drive at work has two batteries.
 
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Old Dec 4, 2012 | 12:33 PM
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That's what i figured - thanks

Is there a primary/secondary

Does one supply more than the other during regular operation?
 
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Old Dec 4, 2012 | 01:01 PM
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The passenger side one is considered the primary battery, but they are both directly linked together, so they work in unison.
 
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Old Dec 4, 2012 | 04:06 PM
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I believe the owners manual says to jump start from the passengers side battery.
 
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Old Dec 4, 2012 | 04:34 PM
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The batteries are wired in parallel but as others mentioned, Ford considers the passenger battery the primary.
That's where I pull power from when needed (such as my viair air compressor).
 
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Old Dec 4, 2012 | 05:48 PM
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If you live in a colder climate by the time the glow plugs go through their cycle. And then try to start the truck one battery would not cut it.

Glow plugs take a lot of juice out of battery.
Also in the winter time the diesel engine crank a little bit longer to get started.
 
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Old Dec 4, 2012 | 06:24 PM
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Thanks for the info guys really appreciate
 
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Old Dec 4, 2012 | 07:50 PM
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Crazy discussed this a long time ago but this image is why the glow plugs need battery power.

You don't reach over 2,200°F in two seconds without sucking up some power.
Not to mention there's 8.

 
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Old Dec 4, 2012 | 09:02 PM
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That is amazing
 
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Old Dec 6, 2012 | 11:20 AM
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And, when it comes to replacing the batteries, always replace both at same time. Even if only one is bad.
 
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Old Dec 6, 2012 | 12:28 PM
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Originally Posted by sgrol
And, when it comes to replacing the batteries, always replace both at same time. Even if only one is bad.

Thus is an absolute must!!!!! Sgrol, two thumbs up
 
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Old Dec 6, 2012 | 07:43 PM
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Originally Posted by McFarlandkm
Thus is an absolute must!!!!! Sgrol, two thumbs up
Yep! You will pay for it later if you don't.
 
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Old Dec 8, 2012 | 06:37 AM
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Thanks those are some things I always wanted to know too.. This is my first Diesel truck too..
 
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