The Trojan link has good info.You're saving $1000 is meaningless to us without knowing how many and what size batteries you're getting. If you're buying 2, 4 or 6, big difference in percent of savings. Load test less important to house batteries, specific gravity more important. Be sure you can decode the manufacture date stamped into the battery case or terminal, not the sticker. Ask if the owner did overnights or weekends (2 nights). Did they come out of a boat? They could be from other devices. Do they have a generator or inverter? What appliancess did they power? Ask to look at the new batteries that took their place. Do they match the reason the seller gave you for replacing perfectly good batteries, and why after 2 years? I applaud you for considering this route, especially if you're not keeping the boat for more than another couple of years. But if you're keeping it over about 4 years, I'd buy new for peace of mind. Please let us know what you discover from your investigations. Cheers.