[Eris (Gerard)]

Hi everyone,
Taking the risk that this post is too obvious I am looking to transport my Skywatcher HEQ5 Pro mount system and Atik One 6 beyond the city lights and powered up from a 12 volt deep cycle battery. I require the battery to have sufficient power to last a good night of observations with something left to spare.
Can anyone please advise me of things I need to consider before making a battery purchase?
Thanks to all who are able to offer advice.