No electrics but have engine then next day, no engine and no electrics either!

What is your question?

This has happened three times over past couple of months. I drive the car as normal, get home and next day no electrics but engine turns over , day after that the engine won't turn over either. Call out rac, they start it and everything back on. Car works for a few days then it starts all over agin. The garage did a diagnostic check and changed the ignition/ light stalk but that's not worked. Any ideas before I just sell it, it's driving me mad!!