I'm using two two-cell Li-ion packs in parallel in my Double Vision for redundancy. This is the first time I've used this technology. I connected each pack to a switch and then to a 6 volt regulator and then to a single receiver. After flying all day I discovered that power was drawn from only one battery, the other battery was fully charged. I test each switch before every flight and the servos work fine on each individual pack/switch. I charged up the batteries and did some more testing. On a 1 amp load, each pack tests out at 8.17 volts. The output of one regulator is 5.99 volts. The output of the other regulator is 6.01 volts. The only thing I can figure is that this slight difference in regulator output voltage is enough to draw current from only the regulator/battery putting out 6.01 volts. Anyone else run into this problem? Solutions?

My solution was to run a parallel connection between the two packs before the switches.