Plugging one of these into a charger will also let you know if it’s a float or a trickle charger 
On a float charger it will kick on and off endlessly until you plug it in to the skateboard battery.
On a trickle charger it will just turn on and go to full voltage.
Most of the time float is better for skate use because it’s not roasting your cell balancer resistors while it’s plugged in and fully charged.