Late starter

You have load tested the battery at a auto parts store for free I suppose?

 

'Tis the 12V low battery season, as winter approaches. And at 5 to 6.5 years old, the original 12V is getting old if it hasn't yet been replaced. While it is not guaranteed to be the culprit, it is the first item on the suspect list.

If you have a voltmeter, use it to check the voltage before the car is turned on to Ready in the morning, or when the car has been turned off for at least a few hours.

 

It seems that you'r facing the Aux Battery syndrome.
Replace it for an equivalent one or better (Optima yellow top was my choice)

 

That sounds like your subconscious calling.

Assuming that's the original battery, could very well be time. Be careful when battery shopping, the OEM battery has small posts, is AGM type, and has a venting port. It's best to adhere to all that, and keep the same dimensions. Simplest route would be to replace with the same, though there are some aftermarket alternatives: Exide and Optima to name a couple.

You can do a simple check of your battery's at-rest voltage with a digital multimeter. Or more in-depth analysis with a battery analyser, such as Solar BA5:



Step one might be to hook it up to a smart charger. My pref is an older CTEK 3300, but there's lots available.