The Q4 has three charging modes with different Amp outputs; there's speedy 2A charging when one battery is inserted, 1A charging when two batteries are charging, and 0.5A charging when four batteries are inserted. The four spring-loaded bays allow for quick and secure installation of batteries. Four LEDs display the current charge levels of your batteries to keep you advised; we recommend you never leave charging batteries unattended. Multiple inbuilt safety protections feature in the Q4 such as reverse polarity protection, short circuit protection, and overcharge protection. All of which help to protect batteries and the user. The Q4 User Manual fully lists compatible vape batteries including; 18500 batteries, 18650 batteries, 20700 batteries and 21700 batteries. We always recommend that you check that batteries are compatible before charging or using them.