Hey, I have a question ... refilling cartomizers ... how do you know when to add, and how much?
You will always want to add more liquid in, before any burning taste comes.
Normally you will get diminished flavor, and you know it is running low.
But depending on the size of the carto, about 20-30 drops will fill it the first time.
Then each refill should be 10-20 drops.
What you can factor is refilling when ever you get a chance.
i.e. before driving anywhere, before going out, etc.
You will generally get used to how long it will last until flavor fading.
A lot of variables can change the time, as some take small hits verses the power hitter of a 10+ second hit.
Also, when looking inside a carto, you will see the filler either wet or dry.
noticing it very dry, you can add more drops.
Going past the deadline may/will result in a dry or burnt taste.
If you hit the burnt, it may go away, but if not then the burning was too severe.