Easy. Genuine Neato replacement batteries are the best. Costs money. I tried three separate battery packs from other manufacturers including Life batteries which turned out to be the worst! They always had voltage issues: Neato always wanted to charge and showed an orange error light even after charging for days. I'd hit the delete button and wait another two hours while it says it's charging before it deletes. Therefore, battery replacement lifespan is the worst. China's normal aftermarket replacement batteries last about three months and then go to waste. So these OEM batteries are THE BEST AND LONGEST!