In a perfect circuit....with 2 packs wired in parallel....you will have 4.8 volts at 1500 mAh.... The drain from both batteries would be equal.....(voltage in parallel is the same and current is additive)....With 2 packs you want to have 2 switches....so you can charge each pack individually and isolate each battery to make sure both can power the aircraft...
So you go from each battery pack to seperate switches to receiver...one lead in the battery port and the other in any open channel...this will put the packs in parallel....
To check the battery packs make sure you turn on switch 1 and see the airplane power up then turn on switch 2....now when you shut down make sure you turn switch 1 off first and make sure that the airplane remains powered until you shut off switch 2