Thanks for the responses! I did hear back from USABatteryChargers.com. I told them my needs and asked for a recommendation and for a comparison between the H624 and 52PY. First of all, they said that for my more heavy duty applications (I am assuming my super duty truck, skid steer, excavator, etc.) that most portable chargers would not suffice. As for comparing the models, the H624 is the 52PY model on wheels--they are identical but just more mobile on wheels. The 52PY unit weighs 50 pounds so "portable" is somewhat relative. The H624 is probably more "portable" in the end.
Those chargers do in fact do 6, 12, and 24V batteries. Furthermore, correct me if I am wrong, but they have options for fast, medium, and slow charge. I understand what has been said about charging batteries too fast and it not being good for them but if I were in a pinch and needed the battery ASAP the fast charge option would be nice to have.
While I know it is expensive, I am planning to buy the H624 (awaiting responses to this thread before hitting "buy"). It seems like a quality unit that is in many ways the "cadillac" of chargers. I think it would suit all my needs with one machine instead of buying 2 and has all the options I would ever want. In short, it is the most expensive but I think there are legitimate reasons why it is more expensive (namely, versatility). Whenenver I buy a lower end or cheaper model of something I end up regretting it down the road--saving the price of a nice steak or two is not worth it in the long run. I feel like if I buy a cheaper charge that doesn't have the option to charge faster, I will kick myself the first time I need my boat or excavator and have to wait days for the battery to charge.
With that being said, I still profess my relative ignorance and remain very much open to various opinions. Thanks again!