Changing terminal leads on a live battery
An inductor, such as those used in chargers and switched mode regulators have nice ramp currents between switched voltages. But if you interrupt the current, the inductor resists the change in current flow by trying to bridge the gap with increasing voltage created by your disconnection. But since the gaps starts small, the voltage is low ( &lt; 100V) and the arc can stretch with distance sustaining a wide arc but still at a low voltage but continuing the same current.   As long as you weren't touching both terminals or nearby ground wire when it extinguished , no high voltage is transferred to you.  ( There are exceptions )

Normally Air begins to arcs at 3kV/mm and sometimes 1kV or less with sharp points or salt spray even less. But a 10 mm arc starting from zero gap does not mean you are generating 10kV to 30kV because the arc can be stretched with low voltage drop across the arc once ignition has started. 

But nevertheless when the current decays and the arc extinguishes, the voltage will still spike pretty high.  ( Having fun yet?)


  You can keep clear of the metal terminals and exposed conductors with 1~3 cm gap, holding the clean insulation or wear gloves (pref. rubber) or turn off loads before disconnection.