5s and 6s Lipo question

[nastety92]

I'm about to buy some new batteries for my D8T.

Is there a difference between using a single 5s 5000mah battery and using two batteries 2s+3s of the same make, model, mah, c rating?

I ask this question because I would also like to run 6s also. This way I could buy a few 2s and 3s packs and have 5s and 6s confirgurations.

Is having additional battery connections less efficient?

Thanks for the help,
Nick