Solar charger.
This seemed to work - certainly I left the X3 at the airport for 2 months and it started first time even though covered in ice. I had asked them to leave it with the panel plugged in and exposed to sunlight. Unfortunately I have no proof that the valet service did not boost start it the day before. I had a 250 mile run to home before I could get Lotus7's voltmeter unpacked & connected so would have expected that to fully charge.
When at the dealers, I discussed battery problems - their story was that there are a lot of battery problems
They then came out with the story that the X3 needed to be run 40 miles a day to keep the battery fully charged! While I cannot accept the validity of that statement, I do wonder if BMW are suggesting to service managers that they warn customers about future battery problems - this could get expensive for BMW. I got the impression that they were attempting to lay the blame on the customer's driving profile.
My own opinion is that if a 5 mile commute is not enough to keep the car serviceable, then the car is not fit for purpose! I live about 20 miles from the nearest anything so very rarely go for less than a 40 miles excursion - yet service manager was trying to suggest that my profile was of short runs!
As mentioned I did get one of those
voltage monitors used by Lotus7 - nice!
I can see that the voltage readout does vary quite considerably while driving - from 13.4V to 14.8V. On engine braking it seems to vary between 14.62V and 14.80V - the lower voltages occasionally occur while under power.
It would be interesting to know what, if anything, these voltages mean - do they give any indication about the state of charge?
With the voltmeter only connected while the circuits are "active" it is difficult to get an actual static (
unloaded) voltage - looks like I'm going to have to make up an OBD2-connector for the voltmeter.