I have a bunch of Go-cartos that have been refilled 3 or 4 times and are still just as good as new. (I realize that's not a lot, but that's the data I have so far.)
You don't have to count. I do, just to avoid leaking, but I do occasionally lose track and find that the
juice will usually start to drip out of the battery end before it pools on top of the fill (20%VG/80%PG). 90 to 100 drops is usually about right to avoid any dripping.
I haven't disassembled one but they look a lot like a giant version of Bloog's MaxxFusion cartos and perform about the same.