Say you had two (parallel plate) capacitors that were initially charged to unequal charges. If you connect these capacitors in parallel such that the positive terminal of one plate is connected to the negative terminal of the other, what exactly happens to the total charge of the two capacitors? I read somewhere that the charges "annihilate" each other due to the wrong connection and the total charge of the system reduces, but what does that mean exactly? How do charges annihilate each other, and where do they go?
Also if the charge of the system reduces, there must be a consequent decrease in the potential difference between the plates of each of the capacitors. What if this was forcibly maintained by an external battery? What would happen to the charges then?