There is something hinky with that pack. Eight cells for $24 is less than $3 per cell not including the PCB, labor etc - the cells themselves sell for $7. This pack is identical except for the leads and sells for $71. Might be just a typo or something wrong with the description. They seem to have several like that: a 2*2600 pack for $22, a 2S2P 2600 pack for $20 and another 2S2P 2200 for $35. Very odd unless I am missing something.

Not for nothing, but if you need more runtime, rather than a 2S4P ("8 cell") pack, I'd just get a second 2S2P. It lowers the risk of a mismatched cell in the pack acting up.