On Monday, November 5, 2018 at 8:02:04 AM UTC+10, wrote:
I also have heard the stories about fires while charging, but, as far as I know, most involved a different Lithium chemistry (Li-ion, Li-Polymer etc..) LiFePO4 is supposed to be safer, but by how much I do not know. At any rate, I am pretty much stuck with charging them in the plane, as they are mounted well behind the spar, and it takes a good 20-30 minutes to get them out and put them back in.

Here is an FAA report that supports the assertion that LiFePO4 cells are safer: https://www.fire.tc.faa.gov/pdf/TC-16-17.pdf

In their testing, which they admit had quite variable results, they did not get any thermal runaway with LiFePO4 cells, but did with all the other Li chemistries they tested. Note that the graphs in the above article show 1 cell out of 5 consumed by "thermal runaway" but that was the cell that they were heating externally to try and initiate the runaway.

Not to say that you shouldn't take precautions, all battery chemistries store enough energy to start an electrical fire, even if they are relatively immune to thermal runaway and overcharging.