I have that exact starter box with 2 3800 mah batts and it doesn`t last long . If you plan on using it when racing , don`t . At most tracks in my area we have race practice for an hour or two [depending whick track] and then usually at least 2-4 heats and then the mains . Unless your track gives you some time between heats so you can charge the batts , you will not make the whole day . It`s a good box but not with the setup for 2 batteries . I`d get something different and just get a gell cell . I can go two full race days and then some with a gell cell .