Really not sure, I have a 32GB card in mine, I never tried a 64GB. In case it matters, with my 32GB card installed and the camera set on motion detection I can record from 7 am till 5 pm and uses 3.11GB. Here is some info from my first time using it, I had 69, 5 min recordings at aprox 43,000KB on avg. So the total of 69 five min files was 3.11GB. I would estimate .54GB per hour. So a 32 GB card should hold approx 59.25 hours of video and audio. Hope this helps
I used the online video to help. Yes, the instructions are hard to read and understand... that's why the seller made a video. It's pretty easy to understand from there. Go to YouTube and search "Enko 4 in 1".
Not very long. It is a phone battery and can be replaced. I have only had my unit a couple of weeks and keep it plugged in. When I haven't it only last a few hours. Short battery life is a drawback. Works good plugged in though.