Go get trained on modern CPR. The current training is "call for help, get an AED from the environment if you can, the call center might tell you where to get it from, do CPR until the AED arrives, and then follow the AEDs spoken instructions."

If the AED detects it cannot be useful for shocking, it will at least tell you and give you a rhythm to keep doing CPR. So as a casual first aid provider, it doesn't matter to you what the AED can and can't do. Get it, get it hooked up, and let it help you.