Jim,
Another option would be to drop off the old batteries at a local battery place, service station or K-mart. Most will take them, as they can re-sell them to the different battery build places such as Interstate etc., which is a low-end company.
Never purchase batteries from them.
If buying new batteries, the AGM's are the best out there for now. Costs alittle more but I get about 6 years out of them. Easy to charge & they're not supposed to lose more than 5 % of total charge per month. They can't be turned upside down, but if they are on your boat, you have bigger problems anyway.
WHATEVER YOU DO, DO NOT BUY THE UNSEALED TYPE. ESPECIALLY IF YOU LIVE IN A CLIMATE SUCH AS FLORIDA. Some will disagree, but I never have power problems.
They have come out with the new DRY batteries that claim to hold their power for 7 years. My school's still out on this for now, but I read they are making more different size batteries available. I do believe as with any new line, the price is probably alot higher.
CR