He'd probably be better served by getting a better quality flooded type battery, and still save some bucks over going AGM. Or, he could buy a larger house bank, and get longer life by cycling it to shallower cycles. Personally, I can justify a larger house bank but I can't justify AGMs - as fine as they may be. Since I've had my boat, I've doubled the size of the house bank, and will probably double it again if I go electric refrigeration (but I'll probably need a bigger boat to float the batteries!).