Our experience is that the lithium-ion backup batteries for our earlier line of products, and the SV-BAT-320, last up to 5 years easily, but they
are batteries and eventually do degrade to the point that justifies replacement. We did have a batch of bad SV-BAT-320s, and those failed early (well within warranty); that probably explains the failure of your first SV-BAT-320. We warranty the SV-BAT-320 (and the batteries for our earlier products) for 3 years. I suggest you contact our Tech Support group (phone 425-402-0433 or email support at dynonavionics dot com) and explain the circumstances. There were no changes in v13.x to how the SV-BAT-320 is monitored or charged, so we'd like to hear more about the details.
What is the typical life span of the backup battery? I need to get the third battery in less than a year. First one died while building. Second one was fine untill I installed V13 and then it stopped charging even though it passed the backup test. Can't believe these shouldn't last longer that that!