Cellphone battery: bad then good

My cellphone, a modest Motorola, is rather similar to its predecessor. However, from the start, it had rather less battery life, I suspected some software change. Recently, the battery swelled alarmingly, amazing the guy at the excellent Secret City Exchange where I had thus taken it for repair. With a new battery, the battery life is far better. Perhaps that's what I get for ordering a cellphone from an Amazon marketplace seller.