JAVAC REFRIGERANT REFRIGERATION AIR CONDITIONING DIGITAL VACUUM GAUGE VG-64

This uses a couple of AAA batteries, yet stated run-time is 600 hours. The meter responds well and seems accurate, and the only slight downside is that every so often (5-10 minutes) it goes into a self-calibration mode. On the other hand, that it likely what makes it retain its accuracy despite any odd pollution. This is excellent for the job. Interestingly, it seems to calibrate for different gases so the registered pressure doesn't drop by around half when I introduce Argon. Well worth the money.