So not 100% reliable but these are general points:
the cables tend to fail most often. Anker has VoltageBoost which will increase the voltage (a little) to push through a worn cable but that act increases the load on the Powercore. So check your cables!
Lithium Ion technology is much better than predecessors like NiMi and NiCA, but still suffer from deterioration of their capacity over 500 deep cycles. More partial cycle equate to a deep cycle, so 1000 half-drained times of a Powercore of 2000 quarter-drained, are similar.
Heat ages them faster, so if you store them in cooler (but not freezing) places, they last longer.
So pick some example uses:
- A Powercore+ Mini 3300mah if you drained it daily to do one full phone recharge, you'd expect it to be significantly deteriorated after 18 months or so.
- A Powercore 10000, recharging a phone daily, would become partially discharged, so you'd expect it last 5 years. However, if you kept that Powercore 10000 stored on a sunny shelf it would age faster, and not last 5 years, probably 3-4 years.
You have a 18 month warranty, so you see how you'd really have to really use your Powercore a lot to make it die from use before 18 months, but how much longer than 18 months it lasts is a function of how you use it and store it when not in use.
I have about 3 -4 year old Powercores still working, the larger capacity types I tend to now use for home backup power, the newer ones are denser and I travel with. I bought other non-Anker items 3-4 years and they all died apart from Anker. Impressed!