It's not problem. The battery is standard RS-232C coin-type. You can open the synth yourself and replace the battery. Save your patches via cassette port before, if you have something important.
When you replace the battery, you can download the original 106 patch files recorded in .WAV format. Just connect soundcard to Juno's casette port, press Load and play the wave.
I can't remember URL for these patches, sorry. But, I have them on my CD archives. If you can't find them, give me your e-mail and I will send you.
Regards,
Adnan