The wall charger for Joye 510 batteries will last a long time. While it may eventually fail, most of the time there is a simple fix. Unplug the wall charger. Take a Q-Tip and gently clean the contact points around the charger. Overtime, these contact points can get clogged up with residual e-liquid from your batteries causing the unit to malfunction and display a green light even when the battery you are trying to charge is dead. Also clean the contact points on your Joye 510 batteries. You should be able to see that the metal contact points are shiny and clean again.
Most of the time, this should do the trick!