Is the battery user replaceable?
Unfortunately no per XC625 - Battery Backup - Product Details, Specs, Downloads | CyberPower
I mean… if you have a screwdriver… any battery is “user replaceable.” They may not WANT you to replace it, but … 
My first thought when I saw “refurbished” was that the battery was replaced. I mean, what else do you do to refurbish an UPS?
I couldn’t find any pictures of this particular model that shows the bottom. But, I found a similar model that shows the bottom, and it has a phillips screw and ridges to remove a panel.
Presumably it’s the battery cover.
There’s gotta be a way to replace the battery!
Lead acid, find one with the lithium ion. For the size, 9 minutes at half load is not really that good.
Found reviews for a very similar model on the Zon as model ST625U. It’s major difference is that it has two 2.1A USB Charger ports. While it’s also new it costs $30 more than this refurb.
It states: The batteries have been replaced by the manufacturer as part of the re-conditioning process.
And hopefully the fuse is new also.
I guess due to potential liability issues they tell you it’s not replaceable but I’ve never seen one that wasn’t. However the manufacturer can make it difficult to get into it to do a battery replacement, but where there is a need there is usually a way.
Like everything else, these have really gone up in price (and with only 4 battery backup outlets) remember when these were between $20 and $30 New.
Simulated sine wave!?!
TLDR: simulated sine wave is dirty power
From the manufacturer:
Mains AC power from a wall outlet is a true sine wave but most consumer electronics (particularly older or inexpensive items) do not require a true sine wave signal to function properly and are therefore fine for UPS units utilising a simulated sine wave. Simulated sine wave systems use less expensive technology to produce battery power, and are very common in entry/mid-level UPS systems.