A:Answer You cannot have both these battery packs attached to the Joy-Cons and the Switch console itself, not that it matters. These battery packs are meant to charge the Joy-Cons while they aren't connected to the Switch. If the Joy-Cons are connected to the Switch, the batteries aren't being used since it's a direct, physical connection instead of wireless connection. If the Joy-Cons are attached to the Switch while the Switch is being charged, then the Joy-Cons will be charged as well.
How long the packs supply a charge, I cannot answer. I've been using these more as grips than battery packs so I haven't actually put batteries in them yet.
