Is the car near a power point during its rest up?

If so why not simply leave a smart charger connected to keep it topped up.

The down time stated wouldn't be a problem with an old design, but modern stuff never shuts down fully, i reckon it'll struggle to start when you return and most likely to be completely dead, which means either charging from flat or jump starting.

My sisters Volvo truck has never managed to start after a 2 week Christmas break, unless she either remembers to turn it off at the master cut off (still touch and go), and/or goes and runs it for an hour after a week at most...modern reliability, yeah right, it wouldn't last 5 minutes in Siberia...she often ends up jump starting it with her (my old) trusty Volvo 740 td that isn't festooned with electronic rubbish.

Unfortunately my car is in a garage without a power point

how is it then that when you have to change the battery you dont lose the codes

Whenever i change a battery i usually keep a jump pack or similar constant power supply connected to the batt leads and do the changeover carefully.

This is for a variety of reasons, not just codes.

>>If I dont disconnect the battery and it goes flat would the codes not be lost

Too many negatives!

If you don't disconnect the battery and it goes flat the codes probably would be lost!

Disconnecting the battery will be your best option. Most cars place a small drain on the battery 24hrs a day, so if you disconnect it there will be no drain at all.

It will then be down to how good your battery is at retaining its charge.

You may loose codes but they would be lost anyway if the battery goes flat. Modern cars store info in the ECU & don't need codes to be re-entered.