New gadget day. Mentioned recently in a topic about changing batteries, it didn't seem ridiculously expensive and I thought I'd get one and give it a try. It seems it's only available from Thomann at the moment, so I felt obliged to buy something else (an sE V7 microphone, as it happens) to slightly reduce the pain of the £10 shipping.   I've very recently bought an OLP Tony Levin, and the battery in it was a non-name brand of indeterminate age which was still able to make the preamp w