1) The battery does not hold the charge anymore
Batteries are consumables with a limited life span depending on their use. If your battery has undergone more than 300 charging cycles its capacity will be greatly diminished and you will have to recharge it more regularly or acquire a new Power bank.

2) The Power bank does not turn on.
Lithium ion batteries discharge slowly even when you don't use them.
If you have not used the power bank for a long time and its charge level was very low, then the safety system locks the battery to prevent any incident.
When the power banky is locked it will not turn on and it is irreversible.

If your battery does not work for any reason other than those listed above, please return the backup battery to your dealer with proof of purchase. In any case, never throw away your Power bank. We suggest you search on the web for the nearest collection center at home.