40 hours. I think its not just one problem here but probably 2 or 3 combined. I also am not clear what Powercore you got. Did you mean the 26800 PD ? Can you be precise exactly which 26800 you have, a product code off the base? In total, I think there have been about 6 or 7 26800.
This probably has a cable issue, it is the single most common problem, try different cable. Cables have oodles of places they can fail. Anker's cables are excellent but can fail. I did a test a while ago and about 25% of my cables were bad but only 10% of Anker's cables bad, so I only use Anker cables as a result, but 10% is not 0%.
I suspect what is happening is a combination of wrong charger and a bad cable.