Hi N60,
Try this circuit using a10k resistor.
E
Equivalent Schottky used,

 

Perhaps I don't need to worry about 12v on a connector that isn't being used?

Could it damage the battery if the 240v power supply is plugged up at the same time?

Sorry everyone I know this must be quite painful but it really is helpful, so thanks!

 

Hi N60,
Using a high impedance Fluke DVM will give a high reading when connected in that way.
E

I'll have to get my hands on a resistor but I'll give it a go. thanks!