I did preemptive grid charges every 6 months or so as well, with a Genesis One charger (Mike Dabrowski's former personal charger, as it happens), and drove 135 easy highway miles a day five days a week, so lack of temperate balance charging or regular driving would not be factors in premature degradation in my case. Now, balance charging seems to have no positive effect.
Hard to tell what caused mine to fall off the cliff. It's a complex system, so who knows.
I just wanted to get some perspective from the community to get some idea if mine is an unusual case. Thanks for the input, guys.
2001 MT Silver 377K+ mi (Nick) BumbleBee pack, Genesis One charger, KLR3CYL underbody panel, UltraGauge, Calpod switch, 4 speakers, LTMPG 66.0.
2000 MT A/C Silver 218K+ mi (Nora) (clean, maintained recent yard sale find), Dorman reman pack, KLR3CYL underbody panel, UltraGauge, 4 Eclipse speakers.