Repair/Replace Battery Compartment Spring

The best fix-trick I've seen was tinfoil around a snip of rubber band. What you have is a conductive-rubber-ball. It is a common trick with 9V batteries.

For tubular cells, the most common fix requires a similar coil spring from another device.

Using needle-nose pliers, bend the spiral coils tighter to mesh into the old corroded/broken spring.

That eons-old design required you to slide the battery back to compress the spring, thus freeing the positive end for removal. Nobody does that.... just... rip them out. These fixes will fail if you do.

Lack of old spring coil. If the old spring is nearly gone, try the tinfoil-ball trick.

If that fails, coil the new spring to look like a wasp-nest, with a 'twig' sticking out.

That twig goes into the hole left from the corroded spring.

If that fails, you must open the case, and solder the battery wire to the 'twig'.