Recommended · for beginners
EEVblog #140 - Battery Capacity Tutorial
Why people recommend it
Dave Jones explains what battery capacity ratings mean, how higher discharge current reduces usable capacity and how a high device cut-off voltage wastes charge.
Watch for: one viewer notes it is slightly inaccurate in places
In their words
Watch EEVblog #140 - Battery Capacity Tutorial for more information.
Kamil on electronics.stackexchange.com, Apr 2014. CC BY-SA.
Discussing battery capacity and voltage drop is beyond this answer, but this EEVblog video is an excellent starting point.
marcelm on electronics.stackexchange.com, Jul 2016. CC BY-SA.
You might want to watch this EEVBlog video:
Bimpelrekkie on electronics.stackexchange.com, Jun 2021. CC BY-SA.