If you have access to mains electricity, having a permanently available 12 volt power source to power your mount and other accessories makes life just so much easier. The HEQ5 and EQ6 mounts draw about 2 amps of current which is a fair amount for a battery supply to maintain especially on cold nights but a properly specified 12v AC PSU can supply this current indefinitely. I use one supplied by Halfords and intended for use with their cool boxes but it is capable of supplying up to 5 amps making it perfect for this use. This is the link to the item on the Halfords website.
*** !! PLEASE READ COMMENTS BELOW !!***
It had recently been brought to my attention that some examples of this unit produce a 100v potential at the ungrounded legs of mount tripods. I therefore think it prudent to not recommend this device for this application.