I note that the cigarette lighter socket (and the 12V power socket in the rear compartment of the estate) remains live with the igniton and even the auxilliary items swiched "off".

This means that if you leave (for instance) a satnav plugged in, it will stay charged up - good news.  The bad news is that the car battery will slowly be drained, and this will be the case even if you switch the satnav off (it will still draw current to charge its own internal battery) and its USB (or other 5V adaptor) will continue to draw current even if you disconnect the satnav but leave the USB adaptor plugged in.  The adaptor itself - even if not powering and not connected to anything else - draws current and consumes power 
 
I have actually checked this for a new Tomtom Via 350.
Current draw:
Satnav plugged in and running = 250 to 300 mA, depending (presumably) on the state of charge of the satnav battery
Satnav plugged in but switched off  = 150 to 200 mA, again, presumably, depending on the state of charge of the satnav battery
Satnav disconnected but adaptor plugged in = 7.5 mA

It's a bit of a pain having to remember to not just switch the satnav off but also to unplug it and the power adaptor every time you leve the car.  How easy would it be to find an alternative circuit or connection point to feed the satnav from, which switches off with auxilliaries (such as the radio)?

OK 7.5 mA doesn't sound a lot but that's nearly 0.1 Watt which presumably the car battery can't supply indefinitely!

However there are various other items (alarm system, ECU memory, various other electronic memory and other items) which are permanenty powered by the car battery, and the battery seems to cope (for several days, even weeks) without going flat.  Does anyone know how much drain these other items impose on the battery?  Has anyone had their car battery go flat because a satnav, phone or other item has been left permantly connected?

How effective would a cheap solar panel placed on the dashboard be, in keeping the car battery charged up?  At least you would only have to plug it into the cigarette lighter socket, and not take a lead all the way to the car's battery!  The panel I've got and which I could use has an open-circit volatage of around 16 V, but of course that gives no idea how much current it could feed into a 12 V car battery.  Not very much, I suspect.
 

Have you checked the draw when the car has gone to sleep?

 

a Lot of items will only shutdown after this has happend

How would I be able to measure that?

I can measure the current draw of my Tomtom USB adapter out of the car using a 12V power supply and an ordinary test meter, and this obviously doesn't "shut down".  And the 12V cigarette lighter / power socket in the car doesn't - as far as I am aware - ever shut down - unless anyone a bit more clued-up than me can advise me otherwise.

Just had the same problem. Had to add a switched cigar outlet in the cubby hole under the steering wheel using one of these : 
http://www.ebay.co.u...=item3cce90d73e

Luckily the fuse box is very easy to access just behind the cover on the side of the dash next to the drivers door. There are a couple of switched circuits to choose from.

I have my garmin wired in via a extra cig lighter i fitted bejind the fuse box cover & is wired so it only works when ignition is on,no more unsightly wires running from the unit on the windscreen to the cig lighter.