I'm using 2 devices; Pure Smoker's Protege and Super T Manufacturing's Super 6; both are 3.7 volt devices, but the S6 is capable of running at 6 volts - I doubt I'd ever try that feature, 3.7 is enough for me. Both devices are made in the U.S. and I have 510 and 901 adapters for both. I change out the battery daily, never more. I've never used a cartridge, I drip 2 or 3 drops right onto the bridge. One 'dose' lasts quite awhile (I don't know, maybe an hour, maybe 2, sometimes 3 depending) so its not at all annoying. I really like both devices very much, but favor the Super 6.