[PWS]

Provide back-up for whatever modem the SOS unit uses? I'm guessing (totally!) that it's to protect against such a serious crash that power from the main 12v battery was lost. Presumably that might happen now and again, but surely it would need to be a pretty severe crunch?

 

[PWS]

Same ('partial failure') issue here. My dealer (Cambridge) also says that it's a faulty (?dead) back-up battery, but totally unable to source a replacement for the time being (apparently been on back-order for some time). My Q3 is well over 2 years old now and the fault only recently appeared, so I'm much more inclined to believe that it is indeed the battery rather than a software issue.