Here is how I made a parallel battery adapter. Mostly because I didn't want to wait for an order from Hong Kong, but also because the commercially available parallel adapter uses #14 AWG wire, which is probably too small for my Hexacopter.
I tried to make one with wires, but I was never happy with my soldering.
I had the two male connectors on my bench when I realized that wires aren't needed:
I laid a piece of #12 solid wire across the three connectors as a bus, and soldered them together.
Then used a piece of heat-shrink that I had on hand to hide the burn marks from the soldering iron.
It definitely worked well. I got probably ten minutes out of today's combination of two cheap 2200's.
If you decide to make one yourself. I hesitate putting two high-power batteries in parallel without some kind of isolation.
Never store the batteries connected together. If one cell drops even a tenth of a volt, you have a dead short to the other battery. Use an inexpensive alarm on both batteries so that if either battery goes below 9V, an alarm starts beeping.
gh my phone.