To get the full effect of the Provari, you will need high drain
batteries.
I got a couple of their higher mAh batteries when I bought my Provari. They work fine, with the spacing ring and extended bottom, but do not really give me that much more vape time than the high drain AW IMR 1600mAh batteries that I already had. (The high drain AW IMR 1600mAh batteries need the extended bottom also, but not the spacing ring.)
The 2500mAh's seem to be protected versions of the AW IMR, but with the company sticker over them, it is hard to tell without cutting open a perfectly good battery, which I am loath to do. Sometimes the extra hour or two of vape time is worth it. (The 1600mAh usually only last me 8-9 hours, but I tend to vape more than most, so adjust to your vape style.)
Edit: As dormouse said, they strongly recommend the AW IMR, but also say that the 2400mAh batteries they sell were tested with and work well with the Provari.