Genuine Samsung S4 and Note 2 batteries for $12.25 at Unique Mobiles with promo code
$24 is around about market price on S4 batteries - but in many cases they aren't the genuine ones. Anyone who has a S4 knows that the battery life sucks.
You need to grab the linked promotional code and apply it at step 2 on the check at Unique Mobiles. Bit annoying as Unique Mobiles also have a free shipping on accessories promo code out at the moment but their checkout software wont let you stack codes so its either the 50% off OR the free shipping.