K, I'll put together a tutorial on it. Gonna look for some pictures and will post when I got it ready.
EDIT:
Okay, since I don't have the physical UPS in front of me, I can't remember exactly how to take the cover off, but I believe there are 6-8 screws in the back of the unit (where the plugs are) that come out and the cover should come off. If I'm wrong on this, let me know it's bet a couple years.
When you're buying the batteries, it's best to get the ones with the .250" spade connectors on them since the original wiring harness is for .250". These are also called F2. The smaller .187" will work but not quite as snug of a fit (also called the F or F1).
Once you get the original unit's batteries out, they should look like this (in the pic, the batteries are partially separated):
The batteries are stacked vertical and the light gray separate is lightly tape/glued to each battery. You'll need to split/separate the batteries. If the wiring on the batteries comes undone, it's okay as I'll explain the wiring.
So once you get the batteries separated, its best to note how the wires wrap around that light gray separator as it makes it a lot easily when stack the replacement batteries again (as in, the wires will fit nice and snug and the batteries attach nicely again). You can disconnect all the wires and separate the old batteries. A needle nose can come in handy as it can be a b*tch to unhook the wires sometimes. Below is a diagram of how the batteries are wired together. It does not include that light gray separator in the drawing, but you'll need to use that to stack the batteries. See the above picture on how the wires feed through it.
The key thing to remember here is these batteries are hooked in series. 2 12V batteries in series = 24V. 2 batteries in series means that only one wire directly connects the batteries together (fat yellow wire) and it goes from Battery #1 Postive to Battery #2 Negative or vice versa. Battery #1 will then have the negative wire (fat black one) attached to its Negative post and Battery #2 will have the positive wire (fat red) and the small yellow wire attached to the Positive post.
Since we broke the glue on the gray separator, I like to use nylon tape or packing tape to wrap around the two batteries. Nothing heavy duty, just to keep them together when placing it back in the UPS. This battery pack design is one of the poorest that APC every made and it may take you a bit to get all the wires fitting through that gray separator.
Depending on where you are getting your batteries from, they may install them for you. Batteries Plus will, but depending on the store (they are franchises) they may charge you for it, so I can't say. At my store we never charged extra, even if it took 1/2 hour or the batteries swelled up. If you do go to Batteries Plus, the part number for the batteries and the .250 connector is the SLAA12-7.5F2 (or the WKA12-7.5F2). I'd hang on to the receipt and attach it to the unit/batteries since they come with a 1 year warranty.
