i love the Energizer Lithium 9v. i consistantly get about 13hrs. on my mv100 (85mA draw) on a pair w/phantom power on.
when the "Low Battery" light comes on the mv100, i save the used 9v (discharged to roughly 7.5v) and i use three of them for the battery box i made. it holds three 9v totalling 22.5v, so i can use the DC plug for the mv100, which accepts 18-24v. for an all-day festival stealthing, i'll run the battbox.
marc