Energy Loss in Reconnected Capacitors

Two capacitors, with capacitances of $C_1 = 4\ \mu\text{F}$ and $C_2 = 8\ \mu\text{F}$, are connected in series to a 12 V battery. Once fully charged, the capacitors are disconnected from the battery and reconnected to each other in parallel, with plates of like polarity joined. What percentage of the initial stored energy is lost during this reconnection?