The short answer is 8 V and above is a good battery. It’s not the entire answer, the battery typically really starts to spiral down at about 7.4 V that’s about 20% of the power gone, a lot of devices need a bit more voltage to keep them go on. Some devices won’t even work after 8 V. You Kaina Gotta know what you’re Power consumption of your devices as well. In the video I go through the process of testing these 9 V batteries