Charging an EV from an EV

In theory it is possible, the EV “charging” would have to have “charging output” capabilities, such as V2L output, only some EV’s have this, allthough it is getting more common in newer EV’s. The V2L output would be very low though, below 3kw so charging the “out of charge EV” would be very slow, but even a few KW may be enough to get it to a public charger or a home charger

AA have a mobile charger unit which can charge up an EV, enough so they can continue onto a charger. But thats a custom built situation:

https://www.theaa.ie/blog/aas-electric-vehicle-mobile-charging-unit-first-europe/#:~:text=Roadside%20Electric%20Car%20Charging,technology%20meets%20the%20growing%20need.%E2%80%9D

bjorn nyland on his YouTube videos uses a portable charger on some of his range tests seems to be an off the shelf job could be from one of his sponsors portable battery pack

I've done it, just not very quickly.

My brother's Nissan Leaf reached a non-functional charger and couldn't make it to the next one. My MG has vehicle-to-load capability, and I have a cable for it; he plugged in his granny charger, which allowed him to reach the next charger after about 90 minutes of charging. We did this because our mother was with him, and the call-out service was overloaded. If this ever happens, the sensible course of action is to call your insurance company and use their recovery service to tow you to a functioning charger - it's usually free.

Some companies sell a V2V cable - I'm reliably informed (symphonyev.co.uk - they make custom cables) that they are not safe or reliable.