Ha, in a vehicle like my 88 Supra, switch off the ignition switch, and every thing is off except the hazards and head lamps, have to make sure those two things are off. This was in the pre-always hot era. Yeah, I have to put it in the accessory position to listen to the radio, you can switch on the radio with the Cruze or any new car with the keys in your pocket, always hot. But you can't close your windows without your key or remote, what were they thinking, if at all.
Have an inductive pickup ammeter with 0.01 ampere resolution, first step, will quickly learn it takes about five minutes to everything to go to sleep as they say, but some stay awake and can quite awhile to find exactly what it is, because just about everything is always hot.
Taking about compact spares saving a couple pounds, car batteries also fit into this category, but making the plates thinner and closer together. Also have bits of lead that chip off that causes internal leaks, called a high self discharge rate. With my Cruze battery, practically zero current draw on the battery. Well in the garage with the anti-thief turned off, that sucks extra current, don't leave your car parked at an airport for 2-3 weeks, won't start when you get back. Remote entry also draws a little providing its working okay.
But connecting a digital lab type power supply set at 13.2 volts, even after fully charged was still drawing 2.5 amperes, if it really was a 60 AH battery, but this depends on load and temperature would be dead after 24 hours, even less than this, not enough juice left to crank the starter. With my Cruze after just 30 months.
Went to my two GM dealers in town, would only do a CCA test with a fully charge battery and at 75*F, not at 0*F and said it was good, refuse to replace it, found a 3rd dealer that had that GM approved battery tester and after ten minutes said it was bad and replaced it.
If you got five years from your battery, way above average.