I bought a 3-pack of nightlights in December 2021 and another pack in March 2022. These are mainly used to light a stairway at night with two lights linked and the rest as individual. I only charged them when needed. All but one light now only holds a charge for maybe 1-2 days where new they easily lasted 3 weeks.
This seems to be very poor life expectancy being well under a year with a low duty cycle. What warranty do these carry?
Welcome to the community @enr
Curious if you grouped the Night Lights so they come on together? I am asking because battery life is less when you group them. 3 weeks still sounds short, but it depends on how often the lights are triggered.
I use mine not grouped and they seem to last for a few months.
As mentioned, “with two lights linked and the rest as individual.”
The two linked lights are working fine. Of the two which are not holding charge for more than a couple of days one is from my December 2021 box and the other from the March 2022 box. I pulled the final light new from the box to pick up some of the slack caused by the failed lights.
I haven’t experienced any battery issues with the 6 I’ve had since they launched. I did experiment with leaving some linked, but that drained the battery too fast, so now I do them all individually. I’ve come to keep at least one of them plugged in and charging all the time, then when any of the others have a dead battery I just swap them. This makes it really convenient. I haven’t had battery life issues yet though. Maybe it’s because they keep rotating position and so there isn’t one getting used and recharged significantly more often than all the others.
Rotating them is a good idea. In my case they are used on staircases where I could not run powered lights, so if one gets set up they all do as the person walks up/down past the lights. Each one is then used the same as all others, but they are not linked. I have two linked in another area where our dog wouldn’t walk in the dark. 
I’ve worked enough with lithium ion battery devices to know this short of a lifespan is uncommon unless the battery is allowed to overcharge. Best practice is to have a BMS circuit which limits the full charge to no more than 90-95% of capacity.