Got it thx.
I have been chatting to Neil Stratford (@neilstratford) on twitter and he is very skeptical of the figures shown on these apps. He is suggesting that without official confirmation from the manufacturers as to what the numbers mean on theCAN bus then we should not place any reliance at all on the numbers meaning what we think they mean. I am paraphrasing many tweets but I believe that is basically his position (I am hoping he will come over and join the chat here so we can flesh out this discussion further).
I agree with him that the figures involve a lot of guesswork. The manufacturers, especially Nissan, do not publish their CANbus protocols and so it is only by back-engineering and deducing the meanings of each code can these apps be developed. It is not scientific and it is very unofficial. However, I believe that it is possible to back-engineer pretty accurately through observation of the data and comparing it with the real world and that is pretty much what they have done. I accept that it won't stand up to scientific scrutiny but as a driver I don't need that. I just want an indication of what is happening. If the numbers suggest a battery capacity drop of 10.27% and it is actually 10.17% I really don't care. All I need is an indication that it is about 10%. If the figures they use to determine that are not 100% accurate then I really don't care. As long as the end result is a reasonable indication of the truth.
Neil seems to be suggesting that there is no evidence that the battery capacity drops people are seeing with these apps are realistic or at all accurate. Well, everything I have seen to date suggests that the figures are pretty accurate but I am not totally convinced they are 100% accurate. It does depend on the assumptions made by those that back-engineered the code. Having said that, I would imagine that much of the code would be pretty obvious and a sensible deduction could be made as to the meaning based on observation of the real world events.
So, whilst it is fun to play with these apps it is worth remembering that it is just there as a bit of fun and although the figures look sensible to me and I believe the figures to be accurate they could be completely twoddle!
Make up your own minds