Very slim if you get a decent name brand tool set.
They have individually sealed 18650 Li Ion battery cells in them with overcharge and heat and short circuit protection and charge balancing circuits built in to the battery and chargers.
The large single cell Lithium Polymer batteries in Phones and tablets and newer laptop PCs and especially those cheap Chinese no name brand Hover-boards are the ones that you have to watch out for. Those can go BOOM in a big way. My old Li Po phone battery was starting to swell so I took it outside and whacked it with a ball peen and it immediately caught on fire and turned into a little flame thrower.
I have a bunch of spare 18650 batteries sitting around for my 3 18650 powered flashlights and I've never had one get hot unless I short one out intentionally. Then they get very hot, real quick and blow the end out of the cell. But I haven't had one catch fire even dead shorted. Once the top pops off and pressure is released they cool down quick. My spare cells are all out of old laptop batteries. I have a couple dozen of them sitting on my work bench that I've been playing around with. Same cells that's in my Porter Cable 20v max Li Ion drill and impact driver set.
I LOVE my little 20v 1/4" impact gun. It has enough snot to tear apart Any small engine. I can literally tear any old single cylinder engine completely apart in under 10 minutes with it. Mine isn't quite as good as the new Milwaukee set but it's very similar to the Dewalt 20v max set.
Edited by EricFromPa, December 17, 2017 - 10:02 AM.