I have 2 batteries for my njoy 4072. One is always charging while I'm vaping on the other. I find that after 2 hours, the battery is rapidly loosing it's performance but my cartridge is still working. I immediately switch to the battery that's been charging, but it never gets a full 4 hour charge like it needs. I wish there was a long life battery! I've been searching the forum, but can't find the info.