What's so complex in handling batteries that there's battery attendant specialty?
Depending on the technology, when not handled properly, batteries may catch fire or even explode. They also almost always contain hazardous chemicals.
I think the battery attendant would be a person to take care of large battery installations. A hospital for instance has backup power from diesel generators, but needs (much!) battery power to bridge the time between a power outage and the moment the generators are up and running. Power to intensive care units and operating rooms in particular should never be interrupted. Keeping such batteries in good condition is literally a matter of life and dead. (I've worked in a hospital which, as a first measure, received power directly from two different power plants.)