The charger is safe to use depp-perfect for me;)
If you (are fast-loading bins outer) only once a battery lodges-all flashing blue LEDs below the battery slots, and finally light up only in what is the battery.
When charging is completed, the LED goes off and the battery / batteries are not overcharged. Done.
If the battery is defective, the corresponding LED will flash every few seconds-I had not yet used-but the security.
The only downside (I think the price OK, these are the 4 battery case) is that you can not charge 9V blocks can-which will continue to make my old charger.