iPod nano 5th gen: Safe to turn on after 2-3+ years?

In the unlikely event that the case looks swollen, then no. A swollen caswe indicates that the battery has swollen and is pushing the case apart. If this is the situation, I recommend that you safely dispose of the iPod; one option is to return it to an Apple store for recylcing.

If you are going to try the iPod, it will probably need to be plugged into a charge source for at least half-an-hour before you see any signs of life from it. Once that happens, let it charge up for a while, then give it a try to see whether it is functioning.

However, if the battery is worn out, the iPod may not even turn on.

Earbuds1234 wrote:

The case was not swollen and when I plugged it in it when’s straight on booting up and worked. The battery still works. But is it safe to use now or will something happen? E.g, black spot, not work anymore?

If it's not swollen, it's not unsafe. But, as the fiend noted, it probably won't work very well.

There is no way to reliably know what can or will happen. A common issue with old players, particularly if they have not been used for a while is that the battery has a very short run time, or simply will not hold a charge. My experience of an iPod with a worn out battery is that it will not work directly from the USB power connection.