Hey all i am looking for some advice in how to go about my project with a Nest Protect gen 2.

In my home i have ran cat6 wire to all 3 locations that require a smoke detector. These cat6 cables are connected to a POE switch for powering the Nest Protect.

The version i picked up for the Nest Protect is the battery version. I am wanting to convert the battery to the POE in order to power it by POE instead of battery. The Nest Protect uses 6 x AA batteries that equal ~9vdc total.



I am converting the POE to 9vdc via a converter:



However my question is- do I need to wire up the 6 battery placers in parallel or series? It would seem that the Nest Protect AC version has only 3 x AA for power backup. Not sure if that matters in my case or not.

I would like to keep a battery backup just in case the POE goes out for whatever reason. The POE has a battery backup as well.

 

Usually, all you need to do is to find each end of the battery pack and not worry about each cell.
Can you see if only 2 wires run from the battery to the board?
Without having one to play with, it is a bit hard, but I'd try just switching your POE box to 9V out and wiring it to the battery output.
If the POE switch has battery backup, that is all you really need. But you could isolate the sensor internal battery via a diode, and feed the POE supply via another diode (Diode OR the supplies together) or have the POE supply operate a relay that disconnects the battery supply until needed.

The 1N4007 diode stops the battery powering the relay.

There are a few ways to go.