I have a number of Motion Sensors from SmartThings using CR2450 batteries and they go from 100% to 67% then 33% in weeks. Are thses the batteries you all use?
That’s the brand recommended by ST. I have had problems with the original ST motion sensors, perhaps you have a bad one. I’d check with ST support. If it’s still under warranty, they will replace it. I’ve had better luck with Iris sensors.
I will tell you from experience, use the batteries noted by manufacture. The sizing by different manufactures dont make contact to the side battery contact. Having said that Ive only had to replace my batter once in my ST Motion monitor. My multisensors are a different story!
This is one replaced by ST about 6 weeks ago.
Welcome to the family.
I have 2 sensors to sell if someone in interested 
. I don’t use them anymore because of that.
Instead I bought ZOOZ ZSE40 4-in-1 sensor that has two AAA batteries, humidity and lux-meter.
Not that the battery life is really better (I installed it 5 months ago and that’s now almost 2 month I am at 1% remaining… but still it works and doesn’t oblige me to buy Panasonic batteries for no reasons).
Yep, this is the guy!