Sorry to hear about your patches Mum. It is so much trial and error.
Yesterday, I was telling a friend I need to get a Tens, and thought about my old one. Where did it go, why did I stop using it etc ?? About 3am last night, I woke up and went to a wardrobe, and there was the box, bunged away at the back. This morning I have put in a new battery and I am sitting here with it tweaking on my back. I have no instruction book, so that will be trial and error. It says it is a Bio Tens, that's all.
But I have found The Tens Company, who sell all machines and leads, patches etc. I think I will order some new pads/patches, the old ones feel a bit squelchy. So many thanks to you for your replies. Mrs Bouquet