Wall charger takes about 3 or so hours to charge. Cig battery takes about 30-45 mins to charge in the PCC or with the PCC plugged in.
So given the same charger wattage, as to charge a single batt, charging the PPC + Batt is going to take twice as long on the assumption that the PCC batt has the same capacity as the PV Batt. In effect unless you keep your PCC fully charged all it does is take longer to charge...
Real problem when they go and reinvent the wheel, reversing the threads on a M40X, in effect preventing you from getting a charger for the batt.
And it looked like such a promising product :(