Your 510 EGO or Twist battery's lifespan from one charge will depend on the mAh of the battery, and how heavy of a user you are. For example, a 400mAh may only last a few hours or half a day, whereas the 900mAh may last all day.
With the Twist batteries, the voltage setting will also affect the battery life. If you are using your Twist on a higher voltage, this will decrease the battery life. However, if you find you're needing to charge your battery but won't have access to a charger in time, you can drop the voltage down to get a bit more life out of it.
Generally speaking, the 510 EGO and Twist batteries are expected to last at least 2 months but may last longer with good care and maintenance. They are guaranteed for 60 days, so if you experience any issues, please check out our Troubleshooting page or contact Customer Services.