I also have a Luna-Pro and this is what I did. I purchased the Luna Pro Battery Adapter from B&H in New York for my meter. It was designed by Gossen to allow the use of # 357 or SR-44 batteris in place of the old 625 batteries. The adapter also includes Voltage reduction circuitry to drop the voltage down to the correct levels needed by the meter. The silver oxide batteries have a much longer life than the hearing aid batteries and the Wein Cells. At $38.95 it is a little pricey, but it works perfectly and the first pair of batteries is included.

Hope this helps,