Start by measuring the voltage directly at the battery. If you read more than 3.5V, then the iPad should start the boot process. If the volatge is lower then it is possible that the charge circuit on the logic board is not working properly. For an iPad, it's important to use a 12W charging [https://www.apple.com/shop/product/MD836LL/A/apple-12w-usb-power-adapter?fnode=91&fs=f%3Dcharger%26fh%3D4588%252B45d4|brick] because the small one and a USB port can't deliver enough current to properly charge the battery.
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Start by measuring the voltage directly at the battery. If you read more than 3.5V, then the iPad should start the boot process. If the voltage is lower then it is possible that the charge circuit on the logic board is not working properly. For an iPad, it's important to use a 12W charging [https://www.apple.com/shop/product/MD836LL/A/apple-12w-usb-power-adapter?fnode=91&fs=f%3Dcharger%26fh%3D4588%252B45d4|brick] because the small one and a USB port can't deliver enough current to properly charge the battery.
Start by measuring the voltage directly at the battery. If you read more than 3.5V, then the iPad should start the boot process. If the volatge is lower then it is possible that the charge circuit on the logic board is not working properly. For an iPad, it's important to use a 12W charging [https://www.apple.com/shop/product/MD836LL/A/apple-12w-usb-power-adapter?fnode=91&fs=f%3Dcharger%26fh%3D4588%252B45d4|brick] because the small one and a USB port can't deliver enough current to properly charge the battery.