I received it in the mail yesterday and tried charging it, but even with the dual fast charger of my phone it doesn’t appear to have charged up at all hours later.
What happened when you charge it as per instructions?
“Specs pad Input: 5v=3a, 9v=2.5A, 15v=1.4A, 20v=1a pad Output: 5v=3a, 9v=2.5A, 15v=1.5A standard Output: 5v=1.5A size: 3.82 x 3.15 x .87 in weight: 9.17 oz. notes to recharge at full-speed, power Core 13400 Nintendo switch Edition requires a power delivery wall charger (not included). power Core recharges at full speed with the Nintendo switch proprietary charger”
“fast charger” is vague, you need specific the above. Chance are your phone charger is either not working at all or is 10W not 20W.
Also try a different C-C cable.
If you decide to buy a charger then happy to help choose based on other needs.
Did you try different chargers?