Smoke Detectors without batteries (wired) - is this okay?

[Zach Schwarzmiller]

I have been remodeling a triplex. The middle unit has smoke detectors without batteries. There were batteries installed in them, but they were just against plastic, there is no connection to the battery. They were all wired in as shown in the photo's. The building is built in 1998. The other two units had a different style of smoke detector that had wire and battery. Photo here: http://1drv.ms/1UUdfkT - Is this a normal type detector or something odd that should be removed? 

Thank You!