Battery Sulfation - How Long Does It Take?
 

The reason I ask is because I just parked the Electric Booger in a parking lot where I caught the bus, and here it will sit ~30-40% discharged for 3-4 hrs before I drive it a short distance home. I normally charge immediately after driving. Should I worry?

Yes, you will shorten the battery life, by how much? I am not sure if anyone has quantified that, in an ideal world you'd only use the top 20% and your batteries would last for 20 years, but you are coming close... but then letting them sit, so that is allowing the sulphation to harden a little, a battery desulphator will help keep the batteries from aging as quickly, same with keeping an eye on the water level and keeping them warm... cold batteries don't hold as much energy so that 40% is more like 90% if it's really cold out.
Other thing that will keep the batteries from aging is a good absorption charge, 12 to 16 hours of charging to "top them off" will help a great deal in extending their life.
I would also say that a good equalizing is going to help a great deal in helping them living longer, so either over charge them a bit, adding water as needed, or toss a 12v charger on each battery from time to time to make sure that each battery is full and happy, I do this with a dumb charger, so it over charges that battery just a little, on my car I do this every month or two, at work on my electric fork lift I do this twice a year when work is slow.

My batteries are AGMs, so water level is obviously not an issue. I also charge with 12V chargers and float charge every few weeks for a few hours, so equalization is also not an issue.

That shouldn't be too bad, you have AGMs so it isn't as quickly affected as flooded lead acid. From my experience, as long as its not days of sitting that low you should be fine.

Lead acid batteries start to sulphate as soon as they come off the line :)

But seriously there used to be a chart for floodies that showed the rate of sulphation at a given state of charge, looks a lot like a bell curve once you get past 50% DOD.

This bell curve can be fixed with a C200 or better charge. So a little tiny solar charger would fix your sulphation issue almost but not quite completely.

AGMs are much less prone to low DOD sulphation as are gel, so I wouldn't worry about it too much, my car afterall sat at 75% SOC everyday for 8-10hrs without issue with many excessively deep discharges.

Good Luck
Ryan