I was just reading about the question about a 250. I bought one this winter at a thrift shop for $1.50 and it has a 9 volt battery in it with a resistor. I have not used it other than to trip the shutter, so I can't say if it is right, but I assume it is close. There is plenty of room to fit the 9 volt in there. I don't know what the resistance is of the resistor is, but if I can find my resistor card, or maybe just look at the colors I can tell you what is in there. I don't put a lot of stock in my color guessing but who knows I might just get it right. Ric.
P.S. I suppose I could check it with my multi-meter too.