I had similar symptoms when my 08 was 40 months old....especially if I let it sit with the radio on while fiddling with it. The second time it happened I was determined to find cause of the problem.
After 2 checks by the "battery SHOWS 12v" pros, I replaced it with a premium new battery.
get in--buckle up--hang on
"soothing agricultural implement/personal servant/Walter Mitty multidimensional access utility device conveniently travels on pavement when necessary and often keeps me warm/cool/dry/soothed as needed."