... I usually get the low vapor for a very short time before it cutsoff and it is hard to tell whether it is low voltage or low juice in the cart at the time.
That's the way it works with my Go-go's. The last couple of minutes of batt life I get low vapor. I don't know if it's refill time or almost-dead battery time. Then the Go-go goes blinky and the question is resolved. It's recharge time.
In my pre-Go-go days it was never a question. After 3 hours of vaping my KR808 auto battery would give me a couple of low vapor drags and then go blinky. With the Go-go ... I get used to a couple of days or so of vaping and am always surprised when it finally needs recharging. The remaining Go-go in my pocket ... always carry two so I can instantly switch between flavors ... goes blinky within 10 -15 minutes after the first one goes down.
After 10 weeks of Go-going ... I still can't quite believe how good this thing is.