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
I'm fairly sure batteries can't be directly connected to AC or they wouldn't charge in the first place. It'd just heat them up. So if they charged at some point, there has to be something else going on.
Looks like they have a half wave rectifier and maybe some sort of bms on top but it’s hard to say from one pic