''(in your case, assuming you have already tried 1 & 2, your original question would indicate that 3 & 4 are also done)''
In my experience, iPad charging issues follow this pattern:
# Always try another Lightning cable and charger, preferably Apple original or MFi certified units.
# The Lightning cable 8-pin connector should be sitting flush with the housing and completely inserted. If it is not, there could be lint/dust/debris inside the port impeding a proper connection. You can clean it out with a toothpick, fine point tweezers or a dental pick. Just be careful not to damage the pins inside the Lightning Port.
# Check the battery condition with a software tool like 3uTools. If the battery shows signs or wear (less than 70-75% of design capacity), replace the battery.
# Check the battery charging with a USB ammeter. If the battery isn’t drawing 1-2A, depending on the charger and charge state, it may be a bad battery or faulty charging circuit. (On older devices, it’s usually the battery ;>).
# If/when you open the device, check the screws holding the charge port in place (see step 84 of this [guide|107042|guide|stepid=64732]). The ones highlighted can become loose. If they are loose, your charge port flex is almost certainly damaged and will require replacement (micro-soldering required).
# If the flex is good and the battery seems fine, then it may be logic board related. This can be the Tristar IC or in some cases the PMIC. the PMIC is a difficult repair and the replacement part is quite expensive.