To the OP, cheap batteries are a fallacy, your data is worth far more than a decent quality branded battery that's been designed for use in a UPS.
If it's not why are you even bothering with a UPS?
I'll probably work my way around to one of those brands you mentioned. I used to use Yuasa batteries exclusively in my motorcycle, so I'll probably start there. These cheapies from refurbups.com are just something I'm going to try out of curiosity, nothing more. Worst case, they fail (and I'm sure they will, most likely sooner rather than later), I get an abrupt shutdown and have to fix my file server. All the data that I really care about is backed up in multiple other places. Besides, 99 times out of 100, at least as far as I've experienced, an abrupt shutdown causes no harm to the computer except a clobbered filesystem journal that (usually) gets automatically fixed on the next boot. That other 1 time out of 100? Well that would suck, but it's nothing I haven't dealt with before.
I do really appreciate the responses here, and getting a list of brands that people here have tried and trusted in their UPS systems is certainly nothing to sneeze at. However, like many here I suspect, I'm not one to trust a brand name
just because some guy on the Internet said so. Don't get me wrong, a recommendation for a particular brand name here is a great starting point. But I also need to get some first hand experience with a brand before I can fully trust it.
Beyond that, I would love to see some hard technical data regarding why cheap batteries suck, how they're physically different from good batteries, how that affects their electrical characteristics, etc. If you could point me toward something like that, I'd certainly appreciate it. I'm okay with getting my hands dirty and doing my own research, but I just don't know where to start. There's so much marketing BS out there, and so many reviews, blogs, etc that don't even scratch the surface of
why Battery A is better than Battery B. For instance, like I said in my original post, I've looked into what the specs on the OEM battery (W/cell, etc) mean, and have found explanations that make sense, but trying to find affordable batteries that actually list those specs (much less an actual datasheet) is nearly impossible. Most places just give you something like "12V, 4.5Ah", which tells you literally nothing about whether or not it's actually any good as a UPS battery. Which leaves me back at square one, which is just trusting a particular set of brand names.
By the way, you said "a decent quality branded battery that's been designed for use in a UPS", but the other responses here basically just say an SLA is an SLA. What exactly does "designed for use in a UPS" translate to in terms of battery specs, and how do I go about determining this? The cheapies from refurbups.com that I bought claim to be designed for use in a UPS, but clearly you don't think I can trust that. So is there some way of telling UPS batteries apart from generic SLAs other than just believing manufacturer/seller claims, or is it just a matter of going with a manufacturer whose claims you feel you can actually trust?