Hi Alistair, I'm not sure on the guarantee - you'd need to ask Moixa. That said, reports from electric cars show that the degradation isn't as bad as some people feared. See http://insideevs.com/understanding-battery-capacity-loss-from-a-four-year-bmw-electric-trial-veteran/ The Maslow has a battery management system which should prevent any severe stresses. And, I hope, bigger batteries will be cheaper in the future.