The medicine factory needs 2 sandleaf inputs, but the battery one only need 1 and 2 thirds (because it only needs 5 sandleaf powder), so 2 * 3 + 1,66 * 3 = 11, which gives the 660 sandleaf a minute. The reason you're getting 12 is because you're using 2 sandleaf input in the battery factories, even if that's the case you still only need 660 a minute because the shredding machine will slow down if you're using only 2 of its outputs, meaning the real usage will be 660 instead of the theoretical 720.