That's what's called "Value Engineerering".
Costs to the manufacturers are very little between battery manufacturers and are a completely different price in the retail marketplace. The guy who has the OEM battery usually gets to charge more in the retail market.
It doesn't have much to do with quality, more like "will these work, what's our bottom line cost and will they get us through the warranty period".
Club Car like EZGO is fighting both the economic downturn and the pressure from Chinese imports and need to reduce costs to keep the margins up.