You want to rebuild the pre-built coils? Or use the rba deck, or change to a new coil? A new coil, every week or three.. Depends on the wattage, juice and use. If you're using the rba, I change my cotton every 4 or 5 days. If you're rebuilding the occ, probably the same as the original, though for some reason when I was rebuilding the pre-builts, they didn't last as long as when new. I'm sure I wasnt doing the cotton exactly like they do and that's why.