iPhone 5 will only charge and power on for a few seconds?

Hello,

Have an iPhone 5 come into today that "will not charge".

Have swapped out the charge port - no luck.

Have changed the battery with a semi charged battery - powers for about 3-5 seconds and cuts power.

Disconnect original dead battery and reconnect - charges for about 3-5 seconds and goes dead. No charging symbol/etc.

Some sort of chip issue on the motherboard ?

Any thoughts?

Thank you.