Problem is smartphones often only have 2 to 3 hours battery life using internet, so on a longer journey it's not very practical
What smartphone has that poor battery life these days? I've got a high-end device that I use to watch videos at full brightness/HDR and even that gives about 4-5 hours of screen on time (which I happen to think is pretty poor). In terms of overall standby, it's good for an entire day though.
Many phones now have 5,000mAh batteries or bigger, and can go for days. Samsung's Galaxy S23 Ultra - a high end phone you'd associate with being power hungry - has been giving some users over 10 hours of screen on time. That's longer than most people's working day, and would mean the phone being used literally ALL of that time.
I've seen revenue people dealing with people who have had their phone die. In some instances, they're asked to just double check the phone is dead by holding the power button - but then they invent some excuse about the button not working (or they clearly don't press the button while pretending to do so). They also don't look happy if they're offered a power bank to give it a few minutes charge. The body language tells you everything you need to know!
It certainly does seem to be a new favourite excuse, but the outcome is always a PF or MG11, so I am not sure they've thought it through very well.