Long story but explains why this pea tinfoil idea works, whilst at the same time leaving a question I hope someone else can answer . . . . . .
A few months back my wireless keyboard also just packed up completely. I couldn't work out what was wrong but it did seem that when I put the batteries into the keyboard they were sticking out further than before, so it was a bit more difficult to put the battery cover cap back on. I tried a few different things unsuccessfully and then gave up and dumped it in a drawer.
I had another go this morning and had an idea - a bad one, albeit with a postive result - to try and screw or push the battery terminal inside down into the battery compartment, in case the connection had been separated. I did this by putting double-sided sticky tape onto the handle of a wooden spoon to try and push/screw it back down. My 'ingenious' idea had an unexpected outcome in that when I pulled the spoon out I also pulled out the +positive connector from inside the keyboard, leaving the spring underneath exposed.
Now the batteries are in direct contact with the spring and the keyboard works just fine.
Clearly the tinfoil idea is a far better one than my brutal approach but what I'm a bit mystified by is the +positive on the battery can not even touch the metal connector, which is set too deep inside a plastic frame that stops it from touching it. . . . so was there something else inside that has fallen out that the pea tinfoil acts as a replacement for ?. . . . answsers on a postcard please. . . .