Shields never made much sense to me to start with.
Surely as soon as someone stops firing shields go back to 100% as they are a function of power output?
Not necessarily... I think of them more like capacitors... energy stored in a form which, in this case, creates a "virtual hull" outside the real hull. Like a capacitor, if you turn off the power, it will eventually discharge. And if you use it, you have to recharge it.