The Battery on my 2015 RDX died from the lights being left on. I charged it back up and the engine cranked but no ignition. I had to reprogram the radio, the car was not used for 2 days with the dead battery. Before this happened no issues or warning lights came on. This is a well-maintained vehicle. I'm usually good at finding an issue but this one has me stumped. Any help would be appreciated.

 

How old is the battery?
I put a trickle charger on my wife's 2016 when she was away for a week. I went to the car wash before I was supposed to pick her up at the airport and while waiting in line I turned it off (long line). When I went to restart it - it was dead. nAgain this is after having it supposedly fully charged according to the trickle charger. Tried to get it jump started but had no luck. I called AAA and they were able to jump it but upon testing, it showed as discharged @19%. Battery was 8 years old and like you - gave no sign of it being on it's way out. New battery is 13 months old and haven't had an issue since.

 

The battery is 2 years old, I charged it to full. It cranked but wouldn't fire. I found the problem, my wife always makes sure she has plenty of gas. Long story short, she drove it home, put it in the garage and it was out of gas. Im never though that was the issue until I looked at the fuel gauge. Problem solved

 

Ha! All that is required - spark, air and fuel. Glad you figured it out.