The OEMTOOLS Professional Battery Hydrometer uses specific gravity and the number of floating discs to show state of battery charge. This large 16.25-inch professional disc-type tester is accurate down to -40 degrees Fahrenheit, and the battery specific gravity tester provides accurate state of charge levels at all temperatures. Our hydrometer for battery testing prints the specific gravity levels on the tough, see-through body of the battery tester automotive tool. The large floating discs in these car battery testers are easy to read, and each colored disc is designed to float at a different specific gravity, floating more as specific gravity increases. This battery hydrometer tester quickly and easily draws liquid using a one-piece rubber bulb and neoprene tip. The large, comfortable bulb on these battery testers for cars draws liquid with just one squeeze, providing accurate results in seconds. The flexible neoprene tip on our battery gravity tester makes it easier to access hard-to-reach battery cells. This car battery hydrometer features professional-grade construction and glass housing for long-lasting strength and durability.