12V from 48V system

What are the recommended ways of getting 12V from a 48V system?

My bike has 4 x 12V 16Ahr SLA batteries wired in series on a 48V system. I would like to wire in a 12V outlet that will draw about 2A. I know that I could just connect to one of the 12V batteries for my 12V outlet, however that would tend to discharge that battery faster than the other three.

Any suggestions would be greatly appreciated.
One of those will work but you should have a fuse and a switch so that it is not draining your battery when you are not riding. I have one like that on my 48V golf cart.
Thank you for the info. Just what I need. I have found that I can import it from China for USD6 including delivery to Cebu, so I have ordered one. Should be delivered within a week or two.