With remaining Tosas as old as they now are, most are likely suffering from dying backup batteries, so this becomes an even more important topic now than when it was originally posted.
My hunch is that the innerds of the sl6000 family including the backup battery are pretty much the same as for the sl5500, and I know that quickening did successfully replace the backup battery on his collie, although it was intricate surgery. It was a standard coin battery, I do not recall offhand which type, but pretty easily available.
What I am not clear on is whether the original is rechargable, and I am not going to even being to try to disassemble my Tosa now to find out, I will use it until it becomes impossible. But it has been nearing that point for quite a long time.
I still am not certain, whether the Tosa will when when connected to power when the backup battery finally does die. I know with my Collie, once the backup battery finally went, then every time I turned the Collie on, it turned itself off, and I have it tucked away for when and if I get brave and decide to try to perform surgery. Given the collie's lack of usb support, I am more likely to try with the Tosa when the time comes.
