2008 Rogue - Battery/starting issues

[SJEK]

Apologies if this is duplicative at all, but I've been having problems over the past three days and am looking for some (hopefully) quick help.

2008 Rogue SL, getting ready to roll over 150,000 miles. Twice over the past two days, I had the following happen - drove the car normally, stopped and went into a store, upon returning to the parking lot car is dead. No lights at all on the dash. Pop the hood, monkey around with the negative battery cable for 15-20 seconds (originally to check if it was loose at the terminal, which it wasn't), get back in the car and it starts. However, the clock, trip computer and radio presets are all reset, as if the battery were entirely removed.

This morning, when I got in, the car gave me some dash lights, radio, etc. but wouldn't turn over. After flipping back the ignition, the dome lights flickered for a few seconds, and afterward I heard a clicking sound (from both the driver footwell area, and another time the passenger side footwell). I went back into the engine compartment and this time actually moved around the battery under the clamp (sliding it towards the drivers side - its secured pretty well) and then the car started, drove normally.

The battery is only about two months old. My guess was that the negative ground cable was either loose,or perhaps corroded. But trying to look down into the engine compartment, it disappears down next to the battery and I can't see where it leads.
Anyone else ever experience this, or have any suggestions? If I remove the battery, is there any better access under the tray to where the negative cable connects?
Thanks in advance for any suggestions!

[Rogue One]

Sounds like your alternator. You can take your vehicle to an auto parts store and have the electrical system checked.