I haven't read all the posts, but if no one has suggested it and you're looking for a KR808 slim style PV... Spend the money and go with the Bloog MaxxFusion. Pricey, but worth it. Just check the Bloog section of this forum if you need more convincing.
Keep in mind, the batts and cartos are designed to work together, so stick with the OEM parts and don't waver. If you clean your cartos using hot water and a childrens oral medical dispenser syringe, you can get LOTS of life out of a single cartomizer.