I use V4L too. I don't know how many puffs you'll get but they last me around 6-8 hours, about as long as the short battery lasts. I go through 2 carts a day and I was a pack-a-day smoker. Put yourself on their email list - they run great sales from 20 to 40% off every month.
I find the vanilla flavor weak also. In fact, I find most of the V4L flavors weak or strange. It takes a while to find your flavors. Try the Wowboy, Coffee, Vanilla mocha frappe. Get Sampler packs to try many different flavors.
I've tried all their 'highly rated' flavors and actually read through the reviews to understand people's reactions. I do think that some of their reviewers are bs, but you can usually get a good feel for a flavor based on a high number of reviews and what people actually say. Their "Most Popular" sort is bull and when you're on the shopping cart, you can't see the ratings.
The flavors have changed over time for me. I suspect that happens a whole lot, one day you love it, the next day you can't taste anything. Partly it's your tastebuds changing. And partly I think their suppliers are inconsistent in the formulations. I haven't tried any other flavor suppliers but am on the verge of it. (Their customer service is beyond compare, tho, and the shipping is really fast.)
You will notice at some point while vaping that the flavor turns odd. That's when its time to toss it. Its the filter that is drying out, getting hot and has lost any flavor. You said 'refill' so I'm supposing you're using a drip tip. The carts get hotter as they lose juice.
This isn't like smoking, when you pay your $5 to $8 and consume virtually the same thing every time - someone has already put all the details together for you and you just accommodate yourself to their product. Vaping is the other way around.
I got frustrated because of the trial and error nature of it but I haven't had a cigarette since I started last October, it costs me less than half what smoking cost, the benefits far outweigh the inconvenience. It takes time to sort it out.