2nd Gen Motion Detector Battery Dead After 3 Months?!

I installed a Ring alarm system in my house on 17th June, and as of a couple of days ago one of the 2nd gen motion detectors was reporting low battery. As of today, it's showing as dead, but I can see it's still reporting events.How can the battery have drained so quickly? It's not an unusually high traffic area. It's on the landing at the top of our stairs, and it's only my wife and me in the house. It's also not a particularly cold area. Finally, our previous alarm system (Yale EF) had a battery powered sensor in exactly the same location and the batteries only needed replacing at around 3 years.Does it sound like the unit is faulty? Or perhaps the supplied battery was a dud? If this is normal then I'm very concerned about the ongoing cost, hassle and the environmental impact of new batteries every 3 months.