Switched to my phone the same way last month when my tablet cable crapped out at a job in OKC. Grabbed a 20,000 mAh Anker pack at Best Buy and it charged my tablet from dead to full about two and a half times before I had to plug it in at the hotel. One thing that helped me: turn the tablet screen way down and kill bluetooth while you shoot, it stretches the battery a lot longer. Also bought a cheap folding solar panel but honestly it charges too slow to trust on a work day, the pack does all the real work. Just keep the pack in your truck overnight so it's topped off before you head out.