Hello Miguel, first, which date code have these batteries? It's really not necessary to change them too early, only after 10 years. I don't know where to purchase them, maybe this guy, M.J. Lorton gives some help (search Youtube), but please don't follow his video too closely.. one battery per RAM is sufficient to buy, and the date code has to be interpreted correctly.. Anyhow, the change with instrument running should be really uncritical.. in case of loss, you need to desolder the CALRAM, insert a DIP precision socket, and program the saved data into the nvRAM (with fresh battery) by universal programmer. If you want to change the batteries of the other two RAMs also, there is no need to save / restore their content, you might only lose setup and programs, which you can both re-program manually, or over GPIB. @Poul-Henning, I've asked you for that assembler code in the past, but only got a Danish 'No' each time. This reason, about copyright violation, I fully understand and accept. Meanwhile, I got a TL866 programmer.. Frank