just thought i'd add my experience. I started with the 808 5 months ago. I used 2 different batts, from 2 different vendors (neither from v4l or premium), for about a month and a half to two months. One died around the 2 month mark. This one happened to be from the (slightly) pricier vendor. When I moved on past the 808, I gave my working batt to a friend. This was a cheap-o generic 808. He's still using it, 5 months later. I've seen him drop it multiple times, even into puddles and snow banks, and the thing is still going strong.
Just because a product is higher-priced, does not mean it is of higher quality. When a friend of mine starting vaping, I warned him about expensive rebranded starter kits from companies that don't disclose the actual model number (ie 808, 510, 901). What did he do? He ordered from v2cigs and paid 2-3x higher than what I paid, even for my more expensive batt. My friend, his brother, and his father all got 2 batt kits, and they each had at least one battery die within the 1st week. They were using pre-filled cartos, so presumably it wasn't a juice in the battery issue. Again, higher-priced does not always equal higher quality.
When using these cheaply made electronics mass produced in China, you are going to encounter a wide range of quality. You could order 2 batts from the same vendor, one could be DOA and the other may last 9 months. It is a crap shoot. That's just the way it is.
Also, saying that a battery lasted 2 months, or 6 months, or any length of time, doesn't really mean much. A battery's lifespan (assuming it is not defective and not abused) is based on the amount of charge cycles. If I have 6 batts in rotation, they'll be charged less frequently than if I only have 2. As a result, they will last "longer." If you use a passthrough when at home, at work, or on the road, you will likely get "longer life" out of your battery.