EMB 145 pilot reported receiving a baggage smoke warning and extinguisher bottle inoperative message during preflight. Pilot confirmed no persons were present in cargo compartment.

Narrative

During this event there were no passengers on board; and FO was finishing a walk around. After powering up the aircraft; I started the fire test per the check list. I noticed the baggage button did not light up. So waited about 20 seconds to do a second test. Still the baggage button did not light up. Right after that EICAS showed a baggage smoke warning message; then the baggage button lit up and right after the smoke message disappeared and the Bagg Ext Btl Inop showed up. I was concerned about any smoke in the back so pressed the button; which shut off; and keeping my PIC authority in mind ran back to see if there was anyone in the cargo compartment. I found no one in the cargo compartment. The bags had already been loaded and it all looked normal. I reported this to my FO; and Flight Attendant. The Flight Attendant then was able to tell the gate agent not to start boarding. I then called dispatch to be patched to maintenance in order to report this and write it up in the log book. Maintenance told Me this item could be differed; but would not be able to carry passengers. In the cockpit I reviewed the incident with my FO and determined all actions that could be taken on the ground were taken.My biggest concern was to see if there had been any person in the cargo compartment. Therefor I acted on my PIC authority to inmediately check if there was any one exposed to the event. I was able to see myself that there was no one. And I also spoke to the rampers; and they were able to determine that no one had been in the cargo compartment at the moment of the incident.My suggestion would be to run a scenario like this during training.