Does anyone have a schematic for these CyberPower AVR UPS's? Thank you... Steve_fromKS

Greetings, Bad Cappers! I work in the avionics industry repairing, modifying, and certifying aircraft power equipment (conveerters, inverters, etc). I live and work in Wichita, KS (USA) and enjoy music and movies and documentaries (on occasion). I am pleased to meet all in the forum and will help when and where I can. In my introduction, I would like to ask if anyone has had direct experience with CyberPower 1350/1500 VA AVR UPS products? I had one that required batteries (about 8 years old, I think). Once I replaced the batteries, the unit would start up but would not charge the batteries....