I think 3rd party is probably your only choice at this point. I've had two:
The one from 'Satonaka' fit and worked, but the cells overheated a bit. Still, there was no swelling. (link here)
The one from 'XDJXWJN' fit, worked, and stayed at a...
You need to download the correct app right from DJI'S website, nothing out of the playstore. Here's the link to it: Phantom 2 - Download Center - DJI Phantom 2 - Download Center - DJI
Your right, I forgot about the 500. That would be enough to charge the drone batteries a quite a few times and weigh substantially less. That might be an option for him, they're not cheap but very nice portable power supplies. I got mine last...
I've got DJI Power 1000 that would definitely do the job for you, but it would be a handful to carry around with you. They even make special cables to fast charge most of their drone models. I say most because they don't make a cable for the...