iPhone 6S black screen of death

I have an old iphone 6s im trying to revive to use as an ipod in my truck should it get stolen, I wouldn't care. Phone worked fine but weak battery. Put it away for awhile. Bring it back out, recharge it, but now no screen. Tried the "black screen tricks" like hard reset etc to no avail. I plug it in pc(Win 10) and it finds it sometimes and other times it doesn't...possibly i screwed up Iphone with all the reboots and even tried restoring with older version of IOS. Trying to reset it to factory default on older version of itunes that finds it but says i need latest version. Install latest version and that version won't find iphone. Go back to old version and once again it finds phone but won't reset it. Trying to do this at this point simply on principle. Any ideas or is it a lost cause?

[Edited by Moderator]