I would stay very far away from this "deal."
1. These are UPS batteries, not alternative-energy deep cycle batteries. Those are very different applications with different requirements, and the battery construction is very different. These are made for float service, not cycle service.
2. These are private-label for Powerware UPS systems. You can't buy them new or fresh. So the reason this guy has them is that they exceeded their allowable shelf life and were off-loaded by Eaton. He even says right in the listing they are as old as 6/06, and they've probably NOT been on any kind of regular maintenance charge since then. That's nearly half of the resting life just plain gone. Likely more if they haven't been cycled or equalized.
3. The very different charge/discharge characteristics of these mean that you can't combine them with other types of batteries. You'll need to install and remove them as a matched set.
Lastly, if one were willing to live with all these limitations, why pay money for them? This type of battery is commonly available for free as take-outs from telecom companies all over the world (although the 2-volt units are more common than 6- or 12-volt models).