The batteries in this UPS lasted less than a year. It was because those battery were "no name" batteries, or because they were connected in series directly to the AC after the transformer? Shouldn't they have a rectifier and condenser before that? It seems that in this way the battery is connected to AC 24/7
Agreed. There are open source UPS projects out there if you want to know what's gone into your design, but be sure you have the time to do this right.
Physics doesn't give a fuck.