I have been tasked with finding a Gossen Luna Pro or Luna Six by an instructor I assist. He is not good with E-Bay, as he has a busy schedule and is always outbid at the last minute. He is aware that there is a battery issue on some if not all models. As usual, 625 batteries causing problems for us...... I have used them before, but I am not familiar with the specifics of these meters. Before I start scouring the 'net for one to purchase, what is the basic difference between models, and what is required to power them properly? I am finding reference to the F, S, SBC.... Is there a model I can look for that does not need a $40 adapter? Thanks in advance.