Replacing Batteries in an APC Smart-UPS SMT1500

I bought a UPS (Uninterruptible Power Supply) with dead batteries, let's replace them! This UPS is an APC Smart-UPS SMT1500 with an APC AP9631 Network Management Card. Batteries are 12V 18Ah sealed lead acid, available here, https://www.ebay.com/itm/121016087316 Filmed with a GoPro Hero8 and Rode Wireless Go II. Edited with Kdenlive.