I have Iphone 3gs same issue,
I have iphone 3gs it turns off randomly, it happens when i used sim , and once time it turns off then doesn't turn on until i connect it via charger plugin or usb , and when i connect it via charger and inserted sim it doesn't off , I updated IOS, and also Restore it and use it as a new , but still having prob , Any one tell me what's the prob , is it common issue or any hardware or software , and i don't think so it's battery issue, Help me Please 🙁