Who ever came up with refilling VK carts from the battery end is a genius. I would never have thought of doing that for fear of ruining the atomizer or the battery, but it works perfectly. It's so much easier than prying off the two caps on the other end.
I'd say to start adding drops before you get the burnt out-of-juice taste these carts give because that taste will linger even after you refill if you hit that point.
Also, I was refilling while watching TV the other night, and not paying great attention, I started dripping directly into the battery by mistake :-/. But when you do it right, the e-liquid seems to suck right into the cart and isn't messy at all, which I expected it to be the first time I tried it. Just let the drop touch the opening on the cart while still on the end of the dropper, and everything stays right in the middle and goes right into the cart.
I'd say to start adding drops before you get the burnt out-of-juice taste these carts give because that taste will linger even after you refill if you hit that point.
Also, I was refilling while watching TV the other night, and not paying great attention, I started dripping directly into the battery by mistake :-/. But when you do it right, the e-liquid seems to suck right into the cart and isn't messy at all, which I expected it to be the first time I tried it. Just let the drop touch the opening on the cart while still on the end of the dropper, and everything stays right in the middle and goes right into the cart.