I've heard people talk about flashlights that use two CR123 batteries and built up gas causing it to expload, ruining your flashlight, and possibly your day. Would this flashlight be one in which I would have to worry about that happening?
Your battries must be matched, voltage and manufacturer. Using a fully charged battery with a partially charged battery could lead to trouble. You should check the condition of your batteries with a tester before using them. I also test mine once in awhile after using them.