Touch the negative side and then the positive to see total. Then do one cell each by touching the individual contacts and the ground. Checking voltage is helpful but the real value to know is resistance. I use my charger to check that at the end of every charge. I have a battery currently that has been reliable but now shows a 57 ohm value on one cell while the other three are 4 or 5 ohms. That’s bad and a battery with reduced flight time and not useful for full flights. I’m working on turning my non flying batteries into power supplies for guitar pedals. We got 8 hours on my oldest and worse battery as they are fine for slow rate but no good for burst power the Hex needs.