I'm not a 12v guru, but I don't see how a bad converter would make individual cells of a battery fail.
I'm sure we'll hear from others with better 12v knowledge.
Sherm & Terry w/rescue Eydie (min Schnauzer) & Charley (std Poodle)
SOLD:2015 Jay Flight 27RLS, GY Endurance (E), Days: 102 '15, 90 '16, 80 '17, 161 '18, 365+ '20
SOLD: 2006 Ford F350 PSD, 4WD, CC, LB, SRW, Camper pkg., 375,000mi
Full timing: Some will think you're crazy, some will be envious, just enjoy the freedom!