I put a link to Battery University at the end. Some of the numbers came from there. Others come from cell data sheets (best ones from Panasonic). A lot of this is synthesis over many data sheets and white papers, none of which would by themselves be illuminating to the average battery user, because so much of the data would be cell-specific.

You're right that device manufacturers choose what to name "100%". Generally, cellphone makers are most attuned to people running out of power, so their 100% is pretty close to the real top charge level (not overcharge). They are rated and tested and reviewed based on tests like Walt Mossberg's run standard processes and see how long it runs until empty. The incentive provided by such make-or-break tests is to allow users to fully charge and fully discharge.

Better control and information would be provided if you gave the actual voltages and chemistries, but both are beyond what a normal user would be comfortable using on a daily basis. Internally, we almost always refer to state of charge in cell voltage terms.

Tesla and BMW provide the ability for the user to know and adjust the top of the charge. Tesla's approach is fairly user-friendly, and BMW's is a little more powerful, albeit less user-friendly.