How come, when my iPod is fully charged and then I disconnect it from its charger, it immediately shuts down?

Hi apple supporter, for months now, my iPod has been acting very unfamiliarly which is causing me to feel upset and annoyed. Once my iPod is disconnected from its charger since it has full battery life, it immediately shuts down with no loading signal whatsoever. And then when I reattach it again to my charger, it turn back on automatically and normally, still with full battery life. Why is my iPod doing this? It gives me a disadvantage because I cannot take my device to any special occasions anymore as it acts as a pitch black screen if it is not connected to its charger or a power source. So everyday, I have just left it connected 24/7 to my charger. How come its always full battery but then just turns black right after I disconnect it from its power source? It is not low battery or anything because its always full battery life as I have kept it on charger all the time now. Please tell me what is happening and try to find me a solution to fix this upsetting problem by replying back to me. Thank you