Mine take 2 batteries, also I purchased a similar item to this -
http://www.ebay.com.au/itm/AC-Power-...ht_7009wt_1163
and was able to modify it to work directly off a 12V battery. I was planning making a few of these up as I have a surplus of inverter modules but time is not on my side at the moment. I now run my
mount and camera off a 12V 20AH battery and last all night.
I only use the battery eliminator only. The PSU is in pieces.