This video is accurate.
My work laptop is about 5 years old and lives on the mains all the time that I'm using it. It's only ever off the mains if it's in its case, or I can't use the charger for some reason and the battery life is still about the same as when it was new.
Also, what they didn't say in the video is that the battery has less stress on it if it's not charged to 100%. To help with this, my iPhone allows the battery to be charged to a maximum of one of 80-85-90-95-100% levels, with the 80% level being the best for it and is what I set it to. It's currently at 131 charge cycles and health is still at 100%.
Now, of course, the smartphone being a highly mobile device does get to discharge its battery every day as it's not practical to keep it plugged in for obvious reasons, but I try not to let it get to below about 40% if possible. Note that if charging from this level, it does tend to get rather warm, so I take the iPhone out of its case so it can run much cooler while charging.
I also use optimised battery charging and power it from a lower power charger, both of which slow down the charging process and reduce the heat generated.
All of these things put less stress on it and help it to last longer.
Finally, every so often, iOS charges the battery to 100% to ensure that the charging circuit remains calibrated, which feels like a little bonus.
Here's Apple's advice on its iPhone batteries:
Find out about charging the battery in your iPhone and how you can prolong your battery’s lifespan.
support.apple.com
