As I've mentioned, most starter e Cigs today perform very well, but depending on the actual device, there can be an issue relating to battery life.
This is a concern not just for those that spend a lot of time outdoors, it's also a concern if you happen to be somewhere without access to an outlet or a USB charging source. If your battery dies, then what?
Batteries have a mAh rating, (milliamp hour) and the higher that number, the greater potential for increased battery life. Other factors are the resistance (ohms) of a given coil, and what wattage is being used. Generally, a starter e Cig that comes with a tank, be it separate or part of the device, will be optimised for the best possible performance and battery life.
Most of today's starter e Cig batteries are rated between 650 mAh and 1500 mAh. obviously, try and aim for the highest mAh possible, especially if you intend on using them a lot whilst outdoors.
A 650 mAh battery can provide anywhere from 3 to 6 hours or so of vape time. 1500 mAh may offer up to 8 hours, depending on frequency of vape and again, wattage and resistance. If you're using a low resistance or sub ohm coil, which is becoming increasingly common, a 1500 mAh battery may only last you 3 hours.
The solution to battery life is to purchase more than one, if the unit takes replaceable batteries. In the case of enclosed devices such as AIO's, you will need to buy at least one additional device.