A battery hydrometer is a fundamental tool for measuring your car battery state of charge. That said, the device is only useful if you don’t own a maintenance free battery.
Maintenance free batteries are sealed and can not be tested using a hydrometer.
Below are some of the more commonly available hydrometers. Like most tools, they range in price, quality and performance.
In my humble opinion, temperature compensated hydrometers are the way to go.
Temperature Correcting Hydrometer
The thing to keep in mind is that potentially expensive decisions are made about battery condition using these tools. Getting one that with valid indications throughout the temperature range is important.
Expect to pay about fifteen dollars. They are readily available HERE.
Manufacturer: East Penn / Deka
Budget Temperature Correcting Hydrometer
This one rings in at about eleven bucks and is available online.
The one you see pictured represents just such a hydrometer.
At about eleven and a half dollars, it is priced right in line with other hydrometers on the market. It too is ready for immediate delivery HERE.
Manufacturer: E-Z Red