[Patrick]

In a 5s1p pack by it's self none will balance each other, because they're in series. But when you connect the two 5s1p packs together to make 5s2p then cell number 1 from pack 1 should balance with cell 1 from pack 2 and cell 2 from pack 1 with cell 2 from pack 2 and so on. So balancing a 5s2p pack should be like balancing a 5s1p pack, because the parallel cells will take care of themselves.
That's why you'd also want to have the 2 packs as close in charge level as possible before you connect them, otherwise they will balance each other very quickly.