My first attempt to solve this was to get a RED top Optima battery. Then I really went digging and found the problem was common with owners in places where it can get really cold (BC Canada, Minnesota, etc).
Some report bad ECMs, IPDMs or ECM relays (part of the IPDM). I read where people have taken the ECMs in during the summer and placed them in the freezer to try and troubleshoot (no go) and others have sent them out to companies to check and repair circuit board connections (theory is the cold temps cause the solder to shrink and separate from the board). More times than not dealers are unable to replicate the issue, my guess is they are jumping the vehicle, it warms up the components and issue goes ghost before they even start working.
So I devised the following: I had to wait for the next cold snap which was tonight. Single digits out right now.
Plan was to first test the relay by tapping it with a screwdriver while the car cranked to see if it was failing mechanically due to the cold.
Second step was to remove the IPDM, bring it inside so it could warm up (just needs to get above 16-20 degrees, an hour inside would be more than enough in my case), then reinstall it and try to start. If that failed a replacement IPDM on ebay runs about $70-$120 ish compared to the $23?.00 the dealer wanted.
Next, I would have to take the radio out to get to the ECM, remove the ECM, bring it in to warm up then reinstall and test/start. OR, run an extension cord from the house and run a heat gun or hair drier under the center dash for maybe an hour or more to warm the ECM up (without setting the car on fire of course). If that failed I would have to send the ECM out to one of these companies to do their thing.
In this manner I would isolate the temperature effects on each component one at a time and thus isolate which component was being affected by the cold.
This is where the IPDM (Intelligent Power Distribution Module) is located; passenger side.
IPDM sits under a black cover.
No tools needed to remove, push tabs in with fingers and lift.
This can't be accurate but it was BRICK A** cold outside.
Blue circle=ECM relay. Orange circle=power for IPDM module. Recommend disconnecting the power to the module before disconnecting or reconnecting anything so you don't cause a surge and fry stuff like maybe the ECM which is essentially the brain for the engine.
I seemed to have lucked out. I first cranked it for about 10-20 seconds to confirm this was still my current life situation in this cold weather. I have a remote starter installed so then I triggered it to crank while I tapped the relay with the screwdriver and after a few taps the f*cker turned over. (Dealer wanted $30 for a new ECM relay, had found it on ebay "OEM new" for $6). I disconnected the power connector and swapped the relays, old for new. I then reconnected the power connector to the IPDM and let it sit outside for about and hour to get everything back to BRICK temp (electrical components warm up just from the current flowing through their circuits).
When I went back out I triggered the starter then stood and waited, first crank was a no go (starter does three attempts), second crank was the money shot. (This was two hours ago now, just went outside and tripped the starter before typing this line to make sure I wasn't jumping the gun. Still Brick but fired up on the first crank.)
Not saying that in your case it will be this easy as it could have easily been any of the other two components but I hope my experience can serve as a reference and or guide to help you narrow your diagnostic.
Good luck.