The FP300 product page says the 2x CR2450s will power the unit for “up to” 3 years on Zigbee and 2 years on Thread. My assumption is this is the absolute maximum (turning off radios, etc.).
Comment below with your thoughts on what a reasonable battery life would be in your use case.
Personally, I’d be happy if they make it a year, but I don’t intend to install them in any location that would make battery changes cumbersome.
I think a year is acceptable, 3 years would be awesome though!
Agreed, anything over 1 year is worth not having a cord.
Agreed, I would be okay with once a year battery changes and fairly pleased with anything longer than 2 years. Totally reasonable trade off for not requiring a wire dangling down from the device (which more than likely would be wall mounted in many cases). Plus, no cord = less visually obtrusive = higher spouse approval rating 
Anything over 1 year is perfect. Im waiting for FP300 long time because i cant stand to have a cord with it.
Following!
I agree, at least make it easy to replace
3 years on Zigbee is not to bad.
Plus I am sure there is an entity to check battery life.
CR2450 are not rechargeable…
I don’t like putting so many disposable batteries everywhere…
Over one year is plenty. Two years would be great.
Good point on e-waste concerns. What would be your thoughts on something rechargeable with a similar form factor? I know there are rechargeable coin cells, but they are not generally made for continuous use.
Over a year nice and would satisfy my expectations
I’d be happy with a year. Anything over that would be a bonus.
Anything is better than wired power in some locations. My hallway, for instance, makes it very impractical to wire up a presence sensor so unfortunately I’ve been relying on just a battery PIR sensor. I understand how power intensive constant mmwave would be though and I do like how Meross combines mmwave with PIR for accurate detection so I can’t wait for the FP300, even if I get a year of battery life.
I am just looking to lose the cord, a year of battery is good with me.
I think, as many have said, ONE year should be acceptable. As I’m waiting for a device like this battery powered for a long time, changing its batteries once a year can be done easily. 
I am happy with any device if I can get a year out of the battery
I was expecting around a year, so if it gets close to 2 or even 3 years then I’d take that as a win 
I think the new sensor is intended as an alternative to the FP2. It’s intended for applications where you can’t or don’t want to run a power cable. I think a realistic 1-year battery life is quite acceptable. Keep in mind that there will likely be future software improvements, and the competition might not even have such a product in their portfolio. I’m curious.
Not to use it lol
For me, last up to 1 year is pretty acceptable already.