I have no extra accessories connected only USB charger that I'm using for my mobile when I'm traveling far about 1x month and little digital voltmeter connected to battery. When I had problem I have tracked some voltage deviations to fan but some were unknown probably linked to dying rectifier. I was also investigating what else could lead to rectifier failure other than heat and bad connection but I did not find anything conclusive. When my previous rectifiers died voltage always went up to 18-20v. Another theory I had earlier was that some rectifiers could be faulty from factory but I believe that on Tenere rectifiers basically cooking themselves alive