Well, it's going to depend a lot on how heavily you vape. One KGO (EGO variant) usually won't last me a complete day at work, but it comes close. The conventional wisdom says the average will be about 1 hour per 100 mah, so start with an assumption of 6.5 hours each battery.
If you mean how long before they will not hold a charge well. It should be from 200 to 300 hundred charge discharge cycles.If you mean how long before it needs to be recharged. If using a standard resistance coil 2.4 to 2.6 ohm and at the 3.4 volt nominal voltage you should get 150 drags (puffs) at 10 seconds length. That is if its a 650mAh battery.
My ego mini 400mah lasts me like 1 day of solid vaping. Have about 5 breaks at work plus I'll sneak in a few (bunch) of vapes since it's easy to get away from everyone Sometimes it will die a few hours before bed if I start chain vaping once I get home
My ego twist 1100mah lasts me two days.. I've never had one die on me yet because I always charge it the second night.
and in lifespan, you're talking ~300 recharge cycles before the capacity really starts degrading
Many here believe the two best charger manufacturers are Pila, and then Xtar.
Best batteries are Panasonic, AW, and Efest. Some companies recommend a certain brand of battery because the battery tubes and contacts were designed especially for that brand. For instance, Provape recommends only AW brand IMR batteries for the Provari, the use of any other brand will void the warranty. They specifically state not to use Trustfire and Ultrafire brand.
Before investing in batteries for your mod, find out exactly what type is recommended. Some mods require flat top batteries, others require nipple or button top batteries. The vriable voltage mods generally require high drain or IMR batteries and not the protected batteries.
If my hands are busy, my Provari using AW 18650 IMR will be only half drained at 5:00. If I'm sitting around doing nothing but watching TV and vaping, it will die before bedtime. Frequency of use and duty cycle (time with the button pushed) is the key factor.
I have 4 1000mah eGo batts that are two years old. One won't start the charger anymore, but the threads are toast from screwing and unscrewing atomizers. I had one battery that died after 2 months and still have onegood one that came with my original kit. I charged them all the other day.
Batteries are a consumable item and a cost of vaping. Buy good ones, insist on brand names that are known to be solid, and you will get good life out of them. Even knowing that the AW IMR's can last all day, I still carry a spare if I'm out all day. It never hurts to carry a little plastic box with a spare battery and a spare cartomizer (or a new wick for a Vivi Nova tank). That, and my little 3ml bottle of juice ensure that I won't be stuck and thinking about bumming a cigarette.