Nice job, I'm in the process of rejuvenating an even older Braun Hobby EF3. The 2 cell 4 volt lead acid batteries were standard units way back then, although in 67 that would have been towards the end of common usage as nicads and lead acid packs were available for the Braun F 800.

They were high power units but when high speed slide film was ASA 25, you needed it.