It also seemed to be rather random as to how long you got before it switched to economy.Had the (original) battery checked and was told it was fine.
No need at all to replace it etc. Decided to replace it anyway, and fitted a Silver Dynamic Varta, which has a four year warranty.
Shopping around on the internet it was delivered to my door for under £70 - this for an 096 size.
I'm pleased to report that it has solved the economy issue, so was worth doing.
Moral of this story is that the X7 seems very sensitive to battery condition -even though it may check out fine it can still not be good enough for such a thoroughbred machine