I use 2) 5 cell ni mh with a y harness, through one switch, I have used this for several years on different planes.
to do this the packs must be identical.
I use it due to the number of servos and type, to get more mah out of the system
I have always charged both through the switch charge jack,, and haven't had problems, every fall and spring I take them out and discharge and charge separatly.
With that being said, I am starting to switch over to the LIFE batteries, they hold their charge better and can fast charge. With these batteries, you would only need one, But you could do dual for redundancy, in that case you would want the dual switch set ups.
I have the Hitec Aurora, and it tells me the receiver voltage at all times, and I have never had the alarm go off on any set up while flying, So that helps with a piece of mind when flying. When the batteries start to get low, I move both sticks, and can see the voltage drop significantly. then you know to either charge them, or pack it in for the day.