I didn't 'throw out' my DVD collection, but I did get rid of over 90% of it. Back when Hastings was still in business, I took all of it to them for a 'buy back' (knowing I'd only get pennies on my dollar). I only kept the physical media of things I re-watch often (and have re-watched since I got rid of the rest of the titles).
I went from two cheap multi-shelf Walmart DVD shelves down to a single shelf. Everything else is stored on my Plex server (which is also my NAS), which itself is just a PC with a built in 8-bay 3.5" hotswap cage. :)
I'm just re-using my APC Smart-UPS 750 and a pair of batteries like these. Allegedly the BMS / charging circuits in them are designed to work with charging systems that generally charge up 12v lead acid batteries. The pair of batteries I ordered have the exact same dimensions as the lead acid batteries they're going to replace, and the same connectors in exactly the same location.
I've watched a number of videos on YouTube with folks that have done such conversions (using a wide array of UPS models). Even watched a video where a guy did a short circuit test (the battery he used failed miserably, but didn't catch fire). The cable on my UPS has a built in (and replaceable) fuse, so I'm not worried about an issue with the UPS pulling far more amperage than it should be. Of course, that fuse won't do much good if something inside the battery itself fails, but I suppose that's what home owners insurance is for. :)