I'm going to buy Sony a7rII anytime soon, and I would like to use it for timelapse and landscape photography. I've read that a7rII have cca 300 shots per battery, would it be possible to use external battery pack like for charging mobile phones? Camera costs 3500€ alone, I want to save money on external dependecies like this as much as possible.
I guess the best solution is a USB power bank. Your camera should be able to shoot and charge simultaneously (unlike some other models like a6000)
Video here: https://www.youtube.com/watch?v=EO4f-WOotfM
First of all, when it means 300 shots, it means the average time to compose, focus, and shoot the photo. The sony A7RII is not meant for long time shooting. Normally, any battery bank with a USB cable connected to the Sony camera should work. Even if the battery bank lasts long enough, heating may shorten the length that you can shoot timelapses.