4 years still on original batteries and not a hiccup, I did change the BMS in the first year though as I heard too many problems with balancing of the cells. << very happy customer
That sounds like going to a ridiculous extreme, not that we aren't too lax on such matters here. Three psi over recommended pressure could be due to nothing more that a change in the weather, and is very unlikely to cause a skid on wet pavement. Interesting comments about your 5W-30 experiment. I have difficulty believing it could make that much difference in fuel consumption, unless the weather was extremely cold. According to standards, the difference in viscosity is fairly moderate, roughly a 4:3 ratio or closer.
I think it depends on the usage of the car. If I used 5w30 and did lots of long runs and the engine was always running (like on a motorway), then 5w30 barely affected economy other than at the top end. If I used 5w30 in town driving where the engine was on and off all the time - it barely fired up before switching off a lot of the time - and this is on narrower, shorter, more congested European streets, then the fuel economy was significantly worse than if the car used 0w20. Back in 2010 this was apparent and there were some posts of mine at the time showing the actual drop in fuel economy by about 5-10 mpg when using 5w30 which had been accidentally filled in my car. When it was nearly $9 a US gallon for petrol at that time it mattered. I also found that with 5w30 oil I just could not get a journey mpg average above 51 mpg UK (60? US), but when 0w20 was used I could get averages in the mid 60's and individual trips of 70+ mpg UK (85 mpg US?). I no longer have the Prius now so don't really care, but there are many posts about this subject back in 2010 when the ultra thin 0w20 oil was both expensive and rare. Have fun searching
