I don't know what type of battery you are talking about but my dig cam will be powered by a 6 volt, 8ahr sealed lead acid battery. Now if you are talking about a 6 volt lantern type with the spring clips , yes that will work as long as your setup is 6 volts and make sure you get your + and - hooked up in the right place.Now it would be better to use a aux power port on cam if you have one and if not you have to clip on to inside of battery holder the finale + and - going to cam. I hope somebody else will give you better directions than what I can give.
I am not fam. with the rs pir but brians board power has to be no more than 5 volts and no less than 3.5 volts (I think). What they have been doing is coming off the 5 volt regulator from the pir to power brians board. I have a D370 and run it from the aux port using a 6volt sealed lead battery which powers my pir and D370 with no problem. Hope to get close to a month of power. Should be in the field in 2 weeks . I am using the LowPower MS20 pir.
Jim, I have a picture posted of the RS 49-426 sensor. It shows where you can pick up 5 volts (steady). This allows you to run the timer board directly off the sensor. The 425 is similar. There is a steady 5v off the + side of c2.