I’m not a mechanic

nor do I play one on tv, but when we had similar problem it turned out to be one of two things, both of which you could fix right now yourself for free.
1) The battery cables are not on securely. They may look secure, but be wobbling when you hit bumps. So check that.
2) You have corrosion built up on your battery cables. A little baking soda and water will clean that right up.
Both will cause electrical cut out such as you described.