Batteries die from:
- use, they have a fairly fixed charge cycles, of the order of 500, so 500 empty to full, or 1000 half fills. If you used it daily then that would mean should pass the 18 months warranty, typically nearer to 4 years for cared for.
- heat. The heat is highest as the cells approach full so charging to full does more harm than to less than full.
- non use.
No constant charging doesn’t itself cause an issue.
If you keep a cell connected to charger for long periods there is an indirect risk from an electric power spike managing to get through. So unplug when charged.
Finally, I recommend buy the smallest and lowest cost Powercore, get capacity via multiple, as larger Powercore have more cells and when one of them dies the unit is dead, so over time it’s harder to have dead units with say 2 10000 than one 20000. The folks buying high cost larger capacity Powercore and increasing risk of a failed unit just outside of warranty.
So a good example is supposed you wanted to keep around 25Ah of stored energy for say an assumed one week power outage to keep a phone going. You could buy 3 10Ah Powercore and use one to top up phone over a period like over a week, empty it then charge it, then store it for a few weeks and use the next stored 10Ah, rotate around them, so you’d always have on average 25Ah stored energy. If one died you always had 2 spare and can buy replacement.
A bad example would be to buy 26800 and store it for months for an outage, you’d never know if it had died and if it did die you’ve got nothing.