Those evil, evil devices.
There’s not a single set of cables I’ve ever seen at a local auto parts store that’s worth a tinkers damn. Not a single one. About the only way I know to find a decent set is to either go online, or head over to a heavy truck supply. Possibly also a contractors supply, you never know what you’ll find there.
The hot tip, if you’re not willing to dump a couple hundred bucks into an off the shelf unit, is to make them yourself.
Ideally you have a boat supply or chandlery around you that’ll have the correct battery cable – which, if you’re looking for the ultimate item, is what you want. Marine battery cable, marked BC-5W2 is the stuff. Heavy, oil resistant, corrosion resistant. Not cheap either. The reason that you want this over welding cable, or for that matter regular battery cable – the BC-5W2 is much more corrosion resistant, which translates to having better ampacity after sitting in your tool box for three years. You’ll want to get the heavier guages too, especially if you’re dealing with any long runs of cable. Likewise, find the highest quality clamps. All of this wlll have to be swaged together with either a hydraulic press, or an impact swager.
Also, while you’re at it, make up a couple of ends using 350 amp Anderson Powerpoles. Makes the whole setup much more flexible, especially if you hook a powerpole connector into your existing battery cables, and use that to connect a jumper cable set.
Connect that positive to the vehicle that needs jumping, and clamp onto a good engine ground away from the battery. Purely a safety item – if there’s any arcing when you connect the ground, better that you connect the ground to a location far enough away from any hydrogen coming out of the battery. Hydrogen/acid explosions are a great way to ruin a vacation.
Make sure the vehicles aren’t touching, and fire up the support vehicle and bring it to a high idle, then try to start the disable vehicle. Chances are it’ll start right up, if the battery was the issue. If it doesn’t start up, or is sluggish, stop what you’re doing and re-assess the jumper connections. Try again, you’ll probably get a start out of it.
Set the bad vehicle up to a high idle, and if you have a voltmeter on the dash make sure you’re running around 13.5-14 volts. If it’s a low idle you’re probably going to be making less.