QueenBee said:
Yes, clearly I realize we aren't talking about long term storage. So are you are saying that long term storage is fine as long as it says above 70% but charging and discharging on a daily basis while keeping it above 70% during short term storage between uses is not fine?
In any case something is clearly wrong if the battery only lasts 2 years like the OPs or goes dead even though the car is being driven daily.
I don't have a source for long term storage, you provided that number, I'll take your word on it being accurate.
I'm going to say that if you drive short enough trips then the car won't keep the battery above 70%. I'm saying the car doesn't care what the state of charge of the 12v battery is. The engineers picked a charging pattern and it works OK for some and isn't good enough for the rest of us.
Prius, Leaf, you name it if you drive short trips the car isn't going charge enough to keep ahead of the drain.
The something that is clearly wrong is the charging algorithm chosen at the mothership in Japan. If you can't see that you need to stop focusing on the number 70 and start thinking about the result of a large number of transactions where +x and -y don't equal 0.
Imagine a battery is fully charged at 13.0 and useless for starting the car at 11.0 just for round numbers, now imagine that every time you drive to the car it charges +0.1 and drains -0.2. The net change per trip would be -0.1 and it would take 20 trips to hit the one where you couldn't start the car. Obviously not happening that quickly but it's very close to what happens for some drivers.