What size wire are people using when relocating there battery's to there boot? It's on a Sierra

 

behind rear seat next to Methanol container. The + lead terminates at the front bulkhead with a through insolated terminal its the thickest battery lead I could get. This set-up before the 800+ engine.

 

You'll probably be OK with 25mm^2, but if you've added, for example, electric power steering or a big stereo, I'd definitely go for 35mm^2. Have a look for "hi flex" on ebay.

 

Just use 35mm^2 welding cable.

It's largely only for starting anyway, when the engine is running almost all power is coming from the alternator anyway, with the battery being there for any short big surges.

 

May be worth a look in the breakers to plunder BMW parts, cable and jump start terminals for the front.

 

25mm will be ok for smaller engined cars with little or no major electrical power draws...usually good for around 80-100amps
35mm will be ok for medium sized engine cars and audio systems/electrical current draw upto around 175amps
50mm will be ok for large engines, big audio systems, heavy electrical power draw upto approx 300amps

Also, DO NOT buy CCA cable especially for this application, you want OFC cable. Carries more current, more resistant to heat changes and doesnt break down once it has been compressed or exposed to a bit of water.

Welding cable is ok, but the cable sizes never match the cables that I use...for example, 50mm cable that I use is more like 70mm welding cable...but its MUCH more flexible making it easier to route through the car.

 

I dont think he's going to power a silly sound system or hydraulics etc

No normal car ever would exceed the capacity of a 35mm^2 cable, again largely because the alternator is still providing virtually all the power needed.

If this wasnt the case, your battery would be in a constant state of discharge whilst driving...this is not the case, a small amount of current to keep the system charged is always heading to the battery, not the other way around

The largest draw seen is typically during startup, this is a momentary draw not continuous....well for many Fords it might last a while LOL. Naturally the alternator is not providing any power here at all, it's all leaving the battery and can be a couple of hundred amps. Well within almost any length run of 35mm you'd ever see on a car.

And certainly any lugs or fittings I've ever used with 35mm....have fitted the cable correctly. And I'd be annoyed if they didnt. If you buy cable listed as 35mm, 50mm or whatever and need larger lugs or fittings I'd be pretty pissed as it would indicate crap quality. If they cant even get the sizing right, how would you trust the quality of the copper inside ?

 

I went for the 35 in the end I've no stereo set up don't interest me. I'll put an earth stud under the bonnet there will also be an isolator there as well I measured the cranking amps on a Merc sprinter at that was about 180 so my old Sierra will pull less than that