If I think what they're doing is correct one would have to test every well and in some cases keep that oil separate due to cross contamination such as H2s. No centralized battery's but individual for each well.
You aren't supposed to mix oils from different formations--regulations forbid mixing Mississippian oil with Silurian oil, for instance. (There are some 14 or so different formations in the Williston Basin which produce oil). Mixing sour crude with sweet would only lower the value of the sweet crude, so no one would consider it.
The pad well setups have multiple wells producing from the same formation, or from the Bakken and the Three Forks, and the oil is sourced from the Upper and Lower Bakken Shales, respectively.
Same age, same source rock formation, so separate tank batteries do not make sense in that situation.
One of the attractions for drilling multiple wells from one pad is the savings in production infrastructure (lower cost, one location, one lease road, one pipeline tie-in for gas/oil, etc.).
The Bakken and Three Forks oil is sweet, so no H2S.