My 04 CTT has an ongoing battery drain issue that seems somewhat inconsistent in how frequently it occurs.
The battery isn't old (replaced late 2021) and is a correct spec AGM. If charged it can last up to a few weeks or a few days before going completely flat and not starting the car.
Some noteworthy items that could be related are;
-Headlight wiring degredation (I've ordered replacements) although doesn't look like there's any metal on metal contact between wires
-Keyless entry inconsistencies - buttons on drivers side don't work but do on passenger side. Also the drivers door sensor doesn't activate until you pull on the handle
-Aftermarket Alpine head unit - This looks like a quality installation but maybe something is awry?
Underfloor wiring is a possibility although I have seen no signs of dampness and there are no weird electrical gremlins to speak of, other than the parasitic drain itself.
I will get the battery tested to verify it is still ok although I feel like given the reputation of these cars it will be a drain and not a battery that has died in short order.
Any suggestions or tricks to try would be appreciated.
I think I would start by looking at the keyless entry issues. That seems to be ,from what you have said, the main thing that is playing up. Battery isolator ? That will prove the battery is good if every time you connect it up , it starts ?