@MrsFluff , thanks for your post. The longevity of the battery is designed to last if properly maintained (kept away from liquids, hard weather, extreme hot or cold temperatures below 3°C or above 40°C. The battery will have different life spans based on the usage profile, so we are not able to provide a specific life span for them. The power modes and tools used, length of cleaning, floor types, temperature and a range of other variables all contribute to how fast the battery degrades. 

Hello Summer. I expected an answer from a Dyson affiliate to that effect. While I understand that there are varying factors, there must be an average based upon empirical data. These batteries are very expensive not to mention bad for the environment. I went ahead and purchased the vacuum much against my better judgment because it is for my mother who needs the flexibility of cordless. She has a small apartment with no extreme temps, hard weather, etc… I’m quite perplexed, I must say, as to how the various tools could possibly degrade the battery. I just pray it holds up.