Lots of good info. Few extra points.
1. I believe AGM battery (stock in Busa) voltage profile is slightly different than standard flooded batteries (stock in most cars). If anyone has good data on that, I like to see it.
2. While. desulfators may help some lead-acid batteries recover, my experience is that they won't bring back one that has sat a long time discharged.
3. The Battery Tender does shut-off after the battery is charged. At least one cheaper competitor did NOT shut off, even though it claimed to. That would eventually harm the battery.
4. I believe the self-discharge rate is lower on AGM batteries.