You shouldn't create or implement any handmade adapter/backup connector or power lines (no matter what the forms are). It's better to stick with FCC approved devices when it comes to products from this category. Check the support CD for the manual and the software because in case you will be adding more batteries, the UPS will need to be re-configured. I believe you will need to add batteries in parallel mode, but 12/50AH is pretty much for the UPS.