Dash gauges not working, not starting

I drove to the gas station and filled it up and added some sea foam to the tank. At my next stop when I restarted the vehicle to leave it wouldn't start. The battery is relatively new, and nothing had been left on, but I grabbed my jump box anyway and hooked it up. The van started but sounded different; struggled, so I came straight home so I wouldn't end up stranded. While driving, all dash gauges were flat except the speedometer, and eventually it went flat as well. After getting home I checked the battery and it's good. The vehicle won't even attempt to start now. Haven't tried with the jump box again.
Any ideas?