Two years ago I bought Anker extended battery for Samsung Galaxy S5. I used it during few longer trips while I kept it stored and checked it every 6 months when not used. Yet after two years the battery expanded…

I never had such issue with batteries form Mugen or original ones. I some times encounter expanded batteries like that but it’s usually either really old battery kept in a device or some ultra cheap one. Well, too bad that the warranty is “only” 18 months.