An electronics magazine had an article describing how to make a car battery tester, from a length of steel band commonly used to wrap bundles of large items for transport.
The resistance is very low, so you'll need several feet of the stuff. Hammer several nails into a board. Loop the steel band around the nails, zig-zag fashion. Air cooling is automatic.
You must make a very-low-ohm electrical transition from steel to the battery terminal. This is a challenge, and it is up to you to decide whether to weld copper cables to the steel, or use a nut-and-bolt method which requires clean contacts. Etc.