UPS batteries are kind of like starting batteries is that they are designed for a fairly fast discharge .. But They are AGM's so they should be able to handle a decent recharge as well..
I would look up the battery on the battery maker's web site and see what they say. Myself. I'd not use them... but my reasons are a bit complex... Of course if you get 'em free (discarded because the company replaces them every year or some such) or next to it.. that makes a big difference.