downrigger question
 

Hi,
I bought a new(used) boat that came with 2 downriggers. They are lakesystems multi-trollers. They are electric and come with 110V plugs, but I know they aren't 110. I connected them to a 12V battery, but no results.

I opened them up to see if the connections were rusty, but when I opened one, it was filled with oil. Never saw electric connections embedded in oil before. I was told this is done to prevent corrosion.
My brother-in-law suggested that they may be 24 volt and that I should connect the pos of one battery to the neg of the other. Likewise with the neg.

Any help here would be greatly appreciated.

thanks,