Did you contact Anker? Among the many products I've bought from them, I've had a couple of problematic ones, but have found that in these cases their support has been very helpful and sent me a replacement, even a year or so after the original purchase.

No, but I should have. It broke during a trip out of the country and we needed to replace it then and there. Thankfully, we were in Japan, so we had no shortage of options. I'll keep that in mind if I buy from them again.

You can buy any of theirs that was manufactured in the last 1.5-2 years and you shouldn't have a problem. I wouldn't buy one that was originally made 3-4 years ago just because the cells might have lost a lot of capacity. Like the others said, if you contact them they have great customer support and will often (very anecdotal) send you a free one.

How did it fail? I have a few of the PowerCore chargers and have had no issues.

It stopped charging fully and would no longer power any devices. I just tested it the other day while I was getting ready to recycle some other electronics and it was still doing the same thing.

Maybe the typical one would have broken down after couple of hours?