The Sony a6500 uses the NP-FW50 battery. As widely reported, the battery run time for this camera is extremely low, but for video it's not that bad. I tested the battery using manual focus and video only shooting and was able to shoot for 1 hour and 10 minutes continuously (well with a restart every 29:50 due to recording time limit), so say 1 hour per battery to be safe.
When shooting stills and videos mixed at say a sporting event, I tend to get about an hour per battery also. Unfortunately Sony only makes a single battery charger that is pricey, so I am also contemplating this off-brand charger.
I hope that helps you in your planning!
Chris Stenberg is a travelling filmmaker and photographer who works with some of the world's most influential brands. In his spare time he eats apples from trees, spends time with his family, and goes biking and boarding in the mountains of British Columbia.