Battery drain problem

For some reason my battery drains on my 5th gen iPod classic. I will fully charge it and after 2 or 3 days the battery is completely depleted and I have to charge it again. This is without using it at all. I’ve replaced the battery a couple times now from different suppliers. I put in an iflash quad. I changed from Inline SD cards to a Samsung SD card. I made sure everything is plugged in all the way. What could be the issue?