Remember, two things degrade batteries - heat and load. The former more so than the latter, but they both go hand in hand. The heat is not a data point variable the author has I imagine, but he has a decent representation of state with the graph.
The first MBA seems to have more moments of "drained" battery, represented by the orange/red colours being more predominant on the left side of the graph. This may signify more load being placed on the first MBA than the second MBA.
The second MBA seems to have had an unusual beginning to its life - lack of daily data and perhaps being left in a discharged state rather than charged. Might have some play on the initial degradation of the battery's capacity, but probably not.
The first MBA seems to have more moments of "drained" battery, represented by the orange/red colours being more predominant on the left side of the graph. This may signify more load being placed on the first MBA than the second MBA.
The second MBA seems to have had an unusual beginning to its life - lack of daily data and perhaps being left in a discharged state rather than charged. Might have some play on the initial degradation of the battery's capacity, but probably not.