Why Two Batteries?
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Junior User
Joined: Apr 2004
Posts: 81
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From: Kirkland, WA
Why Two Batteries?
'03 E350 HD 15 passenger van. Why are there two batteries? My van wouldn't start so I removed both batteries and had them tested. The one in the engine bay was bad, the other was fine and had a full charge.
Can somebody help me out and explain why there are two batteries in this van? I'm curious as to what the function of the 2nd battery is.
Can somebody help me out and explain why there are two batteries in this van? I'm curious as to what the function of the 2nd battery is.
Post Fiend
Joined: Jun 2002
Posts: 13,873
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From: Atlanta GA
Because sometimes a battery can't store or send enough energy to run the vehicle's electrical system when the engine is at low RPMs.
This might happen if you have dual zone A/C, headlamps on, stereo on, while towing a trailer with a fuel injection system sucking down 25 amps itself.
> The one in the engine bay was bad
If you have one under the vehicle, that is most likely used to run things with the van off without draining the main/starting battery.
This might happen if you have dual zone A/C, headlamps on, stereo on, while towing a trailer with a fuel injection system sucking down 25 amps itself.
> The one in the engine bay was bad
If you have one under the vehicle, that is most likely used to run things with the van off without draining the main/starting battery.
Last edited by rebocardo; Oct 4, 2007 at 02:40 PM.
Senior User
Joined: Jul 2004
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Originally Posted by drive_old_ride_new
OK, that makes sense. I do have the dual zone a/c.
Thx for the explanation.
Thx for the explanation.
More Turbo
Joined: Jun 2004
Posts: 690
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From: Sweden
The main starting battery does not have a great deal of capacity, and cannot sustain many deep cycles very often. In fact, if you drain even 1/3rd of the starting battery frequently it will not last nearly as long.
The deep cycle has a lot of capacity, and is durable for some fairly deep discharges. But they have a hard time putting out enough current to start an engine. And, well, a deep cycle's important capability of being able to take a lot out of it and run it down means you won't have the power available to start the car again.
The system's set up so the batteries won't run down together. Running down the deep cycle won't run down the starting battery.
The deep cycle has a lot of capacity, and is durable for some fairly deep discharges. But they have a hard time putting out enough current to start an engine. And, well, a deep cycle's important capability of being able to take a lot out of it and run it down means you won't have the power available to start the car again.
The system's set up so the batteries won't run down together. Running down the deep cycle won't run down the starting battery.
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Joined: Jul 2004
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Originally Posted by Desert-Rat
The battery under the van was placed there for towing applications only. they are not linked in a way where they assist eachother with starting. treat the second battery as a deep cycle. once the charging system has charged the main starting battery it will charge the deep cycle battery. in my opinion, these second batteries are awesome. I have tapped in to mine to run all my accessories like dvd player, flip down screens, fans, etc... now I can use all my toys and not have to worry about killing my start battery!
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Junior User
Joined: Apr 2004
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From: Kirkland, WA
Originally Posted by Hired Gun
My 1988 Diesel has two batteries mounted under the hood and either one by itself will start my engine. I'm getting ready to order a V-10 van. Where exactly is the second battery mounted?
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