98 S-10 Blazer 4X4 190,000 km

Hello my name is Kimball. The problem I'm having with my blazer is> When I touch the brake the vehicle shuts off or quits, it usually on happens once or twice a day most times only once.I have noticed that the volt meter flucuates when this happens. The truck starts right back up after a few seconds. Could this be caused by a bad battery?This prblem usually occurs first thing in the morning but also has happened even after the truck has been driven for awile but sat for an hour or so, before starting out for another drive.
Thanks hope you can help. Kimball