>>4239648The aluminum foil is to make the connection between the battery stack and the terminals, not for insulation. I had the opposite problem where the original camera took 2x1.5v batteries but the replacement was a 3v battery of the same size. So I filled in the other battery spot with aluminum foil to make the circuit.
You could start with 4x cr1220s, shove them to the - end and pack the empty space at the + end with aluminum foil to make the connection. The "3v" lithium batteries can start at 3.6v so 4 will make 12-14.4v.
With this old stuff it's really just "whatever makes it work". I'd bet money though that there isn't any real electronics in that flash, just battery, flash cube and hot shoe in series. So there shouldn't be much that can go wrong. I wouldn't put it on a modern camera since 15v on the hot shoe might fry modern electronics.