I'm having a similar issue. I'm new here, and there's 30 pages of this thread, so I'm sorry if this exact thing has been mentioned before.
I have a 2014 SL. I've only had it about six months, used with about 21000 miles on it.
A few weeks ago I noticed the EV system warning light on after charging in my garage overnight. I had washed it the day before and thought maybe something in the charging port got wet. I drove it to work the follow Monday, where it sits in the sun. Came out after work, no lights were on. I assumed it had dried. The next day after being in the garage, not charging, same light was on. I had to leave for work, no time to investigate. After work, no light. This went on for a couple days, baffling me. Regardless of charging or not, in the garage overnight the light came on, and after work, the light was off. I did some research and realized the sun was recharging my battery, which was likely the cause of my light after being in the garage. After a few days, this issue seemed to resolve itself.
A few weeks later (This past weekend), the light came on again and after being in the sun, went back off. This happened last Thursday and Friday. Then Saturday after being in the garage for about 24 hours without charging, my car was totally dead. I made the decision to just buy a new battery, since I was fairly certain the battery was the issue. Probably on the verge of dying and being kept alive by the sun. I got a Optima Yellow Top, because I read it was a good battery for this car. Changed it out Sunday. I've been working well all week, until today (Friday). The light was on again. It was cloudy yesterday and is overcast today. So maybe the sun wasn't helping me as much, but what on earth could be draining my battery?
I'm not in warranty so I'm hesitant to take it to Nissan. Any ideas?
Thanks