A) personal vehicles are generally very far away from where you're working. And crew transport vehicles drop you off and leave you there. They're not always close by either.
B) I don't have to do anything of the sort. I reach into my pocket... pull out the plug and take out my phone. Then when I'm done I put the phone back in my pocket, grab the plug and plug it in -- an advantage of the lightning plug in my phone.. I don't have to look at it to figure out how to plug it in.
It's far more elegant and useful to have an external battery pack to keep your phone battery topped up than it is to wait for your battery to drain completely, turn it off, open it up and swap batteries
An internal battery is only good for one charge before it needs to be recharged. My battery pack can charge my phone (and/or others' phones) multiple times before I need to charge it.
And every time you get a different phone you need to buy extra batteries.. I've had the same external charger for 5 years. You also need to have a charging base to charge both your phone and the external battery at the same time. I just need another cable.
There's nothing elegant or better about swapping a battery just to get more battery life.