It sounds like you have an older iOS device that has been stored and is now having issues with its battery. The fact that the battery is discharging quickly when the device is shaken suggests that there may be a hardware issue with the battery itself.
One possibility is that the battery has become damaged over time and is not holding a charge properly. Another possibility is that there is an issue with the battery connector inside the device, causing the battery to not make proper contact and discharge quickly.
To resolve the issue, you may want to consider having the battery replaced by a repair center authorized by Apple. This will likely require opening up the device and replacing the battery, which should resolve the issue with the battery discharging quickly.
If the battery replacement does not resolve the issue, there may be a deeper hardware issue with the device that is causing the battery to discharge quickly. In that case, you may need to have the device repaired or replaced.
It's also worth noting that since this device is over a decade old, it may no longer be supported by Apple, and you may have limited options for repairing or replacing it. I would strongly recommend you to upgrade to a more recent iPod.