They both are listed as "sale price". In fact there are only a few things listing a 'regular' price. Since Tenergy owns all-battery.com (see whois registration), they most likely order parts from the bat-cave and assemble the packs here.

I agree that Tenergy cells are a cut and a half above most no-name cells, but the detail descriptions dont actually say they use Tenergy cells (just 'high quality' ones), though I'd expect that to be the case. It might be that they over produced certain configurations and have lowered the price because of their time on the shelf, but THAT doesnt bode well either. You'd think if the packs had been on the shelf for 8-12 months they would feature them more to get them to move. Something just seems amiss with packs with the per-cell price at half the going rate of cheapos.

Given how sensitive Li-Ion us to voltage regulation, I'd get a charger for the 2S4P instead of trying to use the MS one.