I recall reading that there is a way to read the power that the M1 is drawing if you have 2 keypads. But you need to put the system into full alarm mode and have everything active at once. You can also measure the power that the M1 is drawing with a multimeter connected between the M1 and the battery while the AC power wall wart is unplugged. But in both cases, the readings you get will not necessarily be an absolute worst case number, which is what you really need to worry about.
Elk provides a power calculation
spreadsheet on their website. That's really the best way to figure out your power draw.
Don't forget to include wired motion detectors, glass break detectors and smoke detectors if you have them as part of your system.
[Edit]:
The current being used by the system can be displayed on the keypad from the System Diagnostics menu, keypad option 86.