Hot days discharge battery?

Had another low charge today (3 bars). Seems to be intermittent. Unless the battery completely discharges, I don't think this is really a problem.

 

I found this thread by searching because we are experiencing the same issue . Sometimes after being parked overnight we will see two bars. When we park the car at night it usually has 6 or even 7 bars as we travel down a 2 mile long hill then only one more mile to home. On the hill we always see 8 bars. We've begun to take notice of the state of charge when we park in the evening so we can pin this issue down. It has happened perhaps 3-4 times per month during the past three months.

It has been hot in California recently but nights are usually cool, in the 70's, so I didn't consider heat to be a factor.

We have not noticed this during the day, just overnight. We always lock the car and I'm sure it has been turned off. It is right outside the window near my computer so I would hear it if the ICE kicked on.

It hasn't happened in two weeks. If we can be sure of the night time charge level and the two bars in the morning we'll bring it into the local Toyota dealer.