iPad only turns on when connected to the charger and has no OS

So I have an iPad 6 that I got recently but it is not working and I don’t know sadly the cause. I do know what the errors are but I don’t know what to replace so that is why I need some help. So the iPad only turns on when connected with cable. Even if you let it on the charger for a whole day, the moment you unplug it, it turns off. This got me thinking that there is a battery issue with the device. The second problem is that when it does turn on, it is stuck on the iTunes recovery page, so there is no OS.

I have opened the ipad and saw some white residue inside. This got me thinking that there has been some water splilled over it but some people online say that this can be a normal thing because of usage. The iPad also has no scratches or problems.

So my question is now, can I be sure that only the battery is not working anymore (since it does show that iTunes recovery screen) or is it also possible that the logic board got damaged. I am asking this because if only the battery is broken, I am willing to replace that. But replacing the logic board is too expensive and I’d rather sell it then since the parts can be reused.

I tried to recover the iPad in DFU mode but it gets stuck in the ‘Waiting for iPad’ section and then returns a 40xx error number. I also cleaned the connectors of the battery but this also gave no luck. (But I assume that if the battery does not work anymore that this does not have any effect).

Thanks in advanced for reading.