If you search around in the BitChar-G and Microsizer section of this forum you'll find there is two modified zz's with dual battery. one of which has a BCG board. QFM put two batteries in a stock zz too.
yes you cna do it a couple ways one put it on the left side (looking down on car)fits nice dont know if it effects turning and the other you have to cut the locking tabfor the charger