Weird icon on the screen, then turns off

I found my old iPod Classic 3rd gen, 15gb model. Battery is obviously dead and nothing happens when I charge it so I opened it and found out the battery is swollen. I took it out and connected the wires to another 3.7V battery. When I press any button, hdd spins up and it shows this “connect dock cable” icon on the screen and it shuts down after a few seconds. I tried a few different batteries, all 3.6/3.7/3.8v but i got same results. I also tried hooking up wires to power supply with no avail.

Edit:

I tried menu+center, menu+play/pause, play/pause+center, previous+hold…etc it just restarts back to same screen.

I have usb to dock cable so I tried connecting it to my iphones charger and plugging it to pc/mac while itunes was running. Same thing.