It seems to me you are going to buy new cam and manually remove IR filter
Am I right?
will the motion detection script work with infrared?
motion detection (MD) works with data which are displayed on LCD (or TV set when you plug cable).
so if you see infrared on LCD(TV set), MD will see it also.
I'm sure all of the ported cameras support MD so I would suggest you to select camera using your preferences.
NOTE: some cameras recently ported may not have MD working
if you are not sure about recently ported camera - check for reports if zebra/histogram works on them (if works - MD works also).
for less power consumption camera usually turns off LCD (while it is idle) - you can disable it using CHDK
pluging the cable into Video/Audio socket will force camera to believe it is plugged into TV set.
it will switch off LCD but will continue to give the data MD wants.
it also will help to save batteries.
I dont remember exactly time how long my batteries last when I make timelapse video but it is 12 hours atleast
my camera - powershot a630.
batteries are nimh 2650 mAh
there are 4 batteries in my camera
I can not suggest anything about additional power supply