I have a Gossen Luna Pro in which I use the battery adapter sold I think by B&H. I sent it to Quality Light Metrics a while back for service. It is about 2 stops off in part of the scale. I returned it, they checked it, said it was fine. However it remains 2 stops off. (I calibrate using Dr. Richard Henry's methodology) and Quality refunded my money. Does anyone know if this is a battery problem or ?