Rebooting loop after repairing

Hi! I'm having 6th gen iPod Classic with 128GB SD-Card and replacement battery. One day, when I opened my iPod I accedentely broke my battery connector on the logic board, it just fall off, but it got fixed in a local service center. Everything was fine until the iPod ceased to charge. It was showing that it charging but nothing really happened, so the battery dead completely and the player just showed infinite charging screen. While opening iPod again, battery connector fall off once more, so I just went back to service center, where they fitted this thing back in a place, but they said about some issues with the battery. When I got home and put my charger in, player began to boot and after couple of seconds screen went to black then boot again and so on. Because of this boot looping process going really quick I can't even go into disk mode. I saw this similar topic: Why is my iPod not charging

but I can't say either I have same issue or something else. What should I do? Thank you.