Can an external defibrillator deliver a continuous charge?
An external defibrillator will deliver a biphasic waveform usually.  This would look like something like this:

The waveform can also be monophasic or triphasic.  So we are not talking about continuous charge.  Current is equal to charge per second.
A defibrillator circuit is fairly simple.  Generally speaking, you would only need a battery, capacitor, inductor, and a set of paddles.  The most reduced version of the circuit would look like this:

When the switch is connected to 'A', the capacitor is charging.  When it is connected to 'B', the capacitor is discharging through the inductor and the paddles.  I am assuming the inductor is there to control/limit the amount of current surging through the paddles.  Current is what will kill you, not voltage.