Crimped, with a die matched to the lug and the cross-section. A properly made crimp is a gas-tight mechanical joint; solder wicks up the strands and creates a stiff point where the cable flexes, which is where vibration eventually breaks it.
At battery currents, every joint is a potential heater, and the technique used to make it decides whether it stays cool for years.
What a crimp does
The tool compresses the lug barrel onto the conductor hard enough to exclude air between the strands. That is what makes the joint gas-tight and stops oxidation creeping in, and it is why the pressure and the die profile are part of the specification rather than a matter of preference.
What solder does that is unwanted
Molten solder travels along the strands beyond the joint by capillary action, turning flexible cable into a solid rod for a centimetre or two. The transition point concentrates every vibration the installation ever sees.
The other joints in the same chain
Ferrules on stranded wire entering a screw terminal, which stop strands spreading and the clamp biting on air. Ring terminals on a busbar, torqued to a figure the busbar maker publishes. Each has a tool, and none of them is a pair of pliers.
How to tell a bad joint later
Heat under load, at the joint rather than along the cable. A thermal check with everything running finds in a minute what a visual inspection misses entirely, and it finds it before the insulation does.
What people ask before they order
Why does a crimp need a matching die?
Because the tool has to deform the barrel around the conductor to a specific shape and pressure. Pliers, a vice or the wrong die give a joint that holds mechanically and conducts poorly.
Is heat-shrink over the joint necessary?
It is standard practice on battery cable: it seals the barrel against moisture and provides strain relief. Adhesive-lined types are used where water is expected.
Last reviewed 16 September 2026