Battery! for serious racing look for FU matched.
I am not sure about elsewhere but in my city i buy some 3000 for fun racing, cheaper, perhaps because here everyone looks to gp3300 or sanyo3300hv so the shops wanna wipe out the old stock 3000!
that 300 difference doesnt matter to me! one crash at the end of the straight road or in the apex i lost the advantage for a 500 difference! and...i dun have to run 8 min anyone, i aint racing