well it keeps it fully charged without overcharging, so kinda switches between on/off. So say the voltage is supposed to be at 14V. the charger will put it up to it, then go into a mode where it floats until it drops to some voltage (say like 13.6 or something, idk the exact #'s) then it will bring it back up

 

The other advantage to using that other than kepeing the battery charged and in good shape is that if you have the stock radio you won't be flippin out cuz you need the code since the power was disconnected