Battery Relocation

Pompey

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Location
Granite Belt, Queensland
Current Ride
2018 Subaru Outback
Current Ride #2
1999 Subaru WRX Club Spec Evo 3
Has anyone considered relocating the 2 cranking batteries to the rear tray? Assuming the batteries weigh about 30kg each, taking 60kg of weight from in front of the front axle to well behind it will not only make a significant difference to the COG but would free up space in the engine bay.
 
To translate/clarify for us folks in North America ( :ROFLMAO: ), by "rear tray" do you mean the bed of the truck?
 
I haven't tried that, but my main concern would be how much power you would lose while starting given the length of the run. Particularly since you have the diesel. But maybe it wouldn't be too bad?
 
I haven't tried that, but my main concern would be how much power you would lose while starting given the length of the run. Particularly since you have the diesel. But maybe it wouldn't be too bad?
Perhaps with bin enough battery cable the voltage drop would be manageable?
 
They say you can lose 2 amps per 25 feet of cable. However you can go with a larger gauge cable and I doubt you would be anywhere near 25' It should be possible to move them. Maybe under the rear bed tucked in nice with a "marine box" to protect them???????? You could have pair of "studs" under the hood incase you need a jump or charge.
 
Perhaps with bin enough battery cable the voltage drop would be manageable?
Some quick searching online and it seems like diesel engines can draw up to 500 amps while starting. Some places are saying 1000 amps, but I don't know if that's pickup trucks or semis.

Assuming 500 amps, and a 20 foot round-trip run (conservative; only 10 feet each for positive and negative), this chart says you would need 2-3/0 AWG. I'm assuming that means two 3/0 AWG wires the entire length? If so, each wire would be 10.4mm in diameter.

I'm not an expert in this, so hopefully some more knowledgeable folks are able to chime in. But it feels like you would definitely be pushing some limits. Though ultimately, ya, with big enough/enough wires it would be doable. Threading them where you want them would be...interesting. :ROFLMAO:

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Some quick searching online and it seems like diesel engines can draw up to 500 amps while starting. Some places are saying 1000 amps, but I don't know if that's pickup trucks or semis.

Assuming 500 amps, and a 20 foot round-trip run (conservative; only 10 feet each for positive and negative), this chart says you would need 2-3/0 AWG. I'm assuming that means two 3/0 AWG wires the entire length? If so, each wire would be 10.4mm in diameter.

I'm not an expert in this, so hopefully some more knowledgeable folks are able to chime in. But it feels like you would definitely be pushing some limits. Though ultimately, ya, with big enough/enough wires it would be doable. Threading them where you want them would be...interesting. :ROFLMAO:

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You would only need to worry about the positive cable. The negative cables would be short and go straight to the chassis. Then find out what the current draw on the 6.7 powerstroke starter is
 
You would only need to worry about the positive cable. The negative cables would be short and go straight to the chassis. Then find out what the current draw on the 6.7 powerstroke starter is
Ah good point. And I guess you can divide the total amperage draw by two since you could do two runs, one per battery, which makes things much more reasonable.
 
You can also parallel multiple smaller wires, which has the benefit of dispersing any heat more than a single wire.

Recommend fine and high strand count, pure copper, tinned wire with silicone jacket. Welding cable as a substitute.
 
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I can add this comment from a recent battery and cable upgrade in my RV. I used 2/0 pure copper cables that are very fine strand, even 2/0 is difficult to work with as far as flexibility and it was pretty expensive at just over $5 per foot. In addition, If it were me, I would want that negative cable to be attached to the engine block and use a redundant chassis ground.

For me, it isn't even worth considering because the bed of my truck will be filled with camping gear 80% of the time.
 
I like the idea of a weather-tight battery tray under the, bed probably mounted to the frame on the passenger side. While you're at it you could add a jumper/charger connection at the front or back bumper with an Anderson style connection. These are examples from Amazon in the US.
You probably have the same or better in Aus.

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