Around the two-to-four-month mark, you'll notice subtle changes. The battery might not last as long between charges. That's normal—all batteries degrade. But if you're charging after every few sessions, that's a sign it's on its way out. Vapor production might also thin out. If you're using the same cartridge, it could be the cartridge, but if you've tried a fresh one and it's still weak, the pen's heating element is fading.

Another mid-life sign is a change in airflow. If the draw starts feeling tight or airy, the internal seals may be wearing. You can often fix this by cleaning the mouthpiece and airway, but if it persists, replacement is probably your best bet.