3.7V 3500mAh Battery topic

I want to buy some extra batteries and i found these

http://www.ebay.com/itm/3X-3500mAh-B...item485e9f2a35

I noticed the Voltage is 3.7V and the original are 3.8V. since i don't understand im asking

Will it affect something?
Will they have the same duration time as the 3200mah original ones?
are they cheaper cause they don't last as long?
or is it only the brand not being samsung?

Thank you.
i don't know if i had to put this post in Q & A or Accessories but here goes.