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 photographer, filmmaker, occasional wordsmith, and traveller. In his spare time you can find him hanging out with his family and/or biking and boarding in the mountains of British Columbia.