Check that the charging pins are dead straight and the contact points on the coil are clean as well as the clamp fitting area.
As you can see from the picture below, my contacts aren't the most perfect surfaces at all

I connect all three units, then switch on the power and observe how the coil reacts as it is usually at this point where you notice something might not be correct with the coil connection, ie; the light may flicker, flash irregularly or not come on at all.
I once saw that the control box was still charging when the other two units were fully charged! I switched off the current, unplugged the leads and connected a different lead to the control box. After 45 minutes it was fully charged.
The best way to avoid any disasters would be to switch everything on at home and check that the battery levels on all three units show a fully charged state. After all, this only takes 30 seconds


Best
Paul