How long is a battery expected to last before needing replacement? Would it reduce the lifespan if the set was always on but plugged in to power?

Hello, Does anyone have an approximate comparison of sound quality to the DT770? Mine always starts crackling with bass in the left speaker. I know what the problem is but I'm sick of fixing it. Thought the Penrose might be a better option for all-round use (music, games, movies, long wear times).