Trust your senses. I pulled up to a job site, and smelled hot plastic a little while ago. I walked around, and could not find anything, so I went to work. A little while later I headed out to my truck to get something... I don't even remember what. When I opened up the side box on my work cap I was greeted by flames. Fun. My big tool bag had fallen over dumping a file across the terminals of a spent battery I had not tossed in the spent pile back at the shop yet. Plastic terminal caps were in place on the battery. I set on fire a large plastic case full of security tips, the handle of my drywall saw, and a stud finder. One of the fancy video ones. I flicked the file off the battery, blew out the flames, and decided I needed to go back to the shop and wash out my side box. Ouch. What a mess. Tools lost probably fifty or sixty bucks, but the entire work cap smells like plastic smoke, and I have to wash out what looks like acid from the box.
Be careful. Even a spent battery can be dangerous. I guess I'm lucky. In (more than) fifteen years doing this I have never had something like this happen, but I have always been careful because I knew it could happen.
Bob La Londe I should gone fishing today.