Tools to test car batteries.

Voltage is not the most important factor for testing car batteries. It is the current and the inner resistance of the batteries. To test a car battery's current, you could use this one (the meter itself has 16.2 ohm when measuring the voltage. When testing the current, the meter itself has 0.1 ohm (it will be red and hot for the inner resistor of the meter. So be careful. Also don't do this for too long (maximum 10-15 seconds, check the manual before using.) :

https://www.harborfreight.com/100a-612v-battery-load-tester-61747.html?

to test the inner resistance of a car battery, you need to have this one (this one could also get CCA of a car battery):