The battery can go at any minute. Or last to a little beyond 1000 cycles. In almost 3 years, it's been through a lot of cycles. In my (limited) experience, exercising a battery like this helps it get closer to 1000 - my daughter's MBA went to over that mark before the "Service Battery" warning came on. OTOH, my wife's didn't reach 400 before the "Service Battery" came on. FWIW, the former runs her battery all the way down before plugging, the latter usually has it plugged in. Ion any event, a new battery, installed from Apple, is $129.