Two non-starts in the last two days.
1. Wife at grocery store at night. Deck opened with no problem. Doors unlocked fine. Foot on the brake. Mashes the start button and nothing. Did get a DIC reading of "No FOB Detected". After several tries, she called me for help. As I was heading her way with a set of jumper cables, she called back and said it started.

2. When I tried to start it the next morning, I did not get a "No Fob" read out but when I pushed the start button, would not start but could hear a faint clicking sound similar to when a battery is dead. Got the same results 3 times in a row. Waited a couple of minutes and it cranked right up. Shut it down and checked the voltage of the battery and it read 12.45 volts. Started it again and took a reading and the volt meter was reading an output of 13.8 volts. Driving it, the DIC indicates it charging anywhere from 13.8 to 14.4 volts. I had replaced the battery 3 months ago because of a wheel sensor not working and the dealer suggested a new battery would solve it. Not. Anyway, took it back and had the battery tested and it read 12.6 volts and 650 cranking amps with their meter. Had them do it 3 times and all the readings were close. They would not replace the battery saying it checks out to be good. Took it to a second shop and they put a "Load Tester" meter on it and it showed a reading of only 10 volts. Borrowed their tester and checked it again when I got home last night and it was reading 12.4 volts but this morning, it is reading 10 volts again under load. It has not failed to start again. Taking it back to where I bought the battery and taking the Load Tester with me to show them. Don't think I will have any luck since they say they have to go by their tester.

One of my questions is, where is the ground strap located on the '13? Cleaned the terminals and used Dielectric great to keep them clean. Scratching my head on what to check next.

Sorry for the long post but wife is afraid she will be stranded again and need to make it reliable again

 

I have one that is doing the same thing and what I did was to get a new one on Ebay. Sync it and it works fine. This is my second one that failed. GMs fobs are not very reliable and seem to fail too often. I paid $74 for one on Ebay. If you still have the second one that came with the car try using it instead of the one that seems to be failing.

 

Are the batteries in the fob replaceable?

 

Yes it comes with a new battery.!

 

That doesn't mean that the OP's has a new battery or that it's replaceable.