I'm also looking into rechargeable 16340 batteries. Are they really that dangerous if you stick with quality cells/charger? They just seem like the right way to go.
For a Malkoff M61 dropin or one of its variants I see no point in using low capacity 16340 rechargables, you are better off with one 16650 *).
As far as harzard is concerned, they are equally potentially dangerous, that is because of their chemistry. However, if you follow some rules you should be good.
Particularly,
- use quality cells, no cheapos
- use a quality charger
- use "protected" cells (but they are thicker and longer due to their additional protection circuits)
- don't use any damaged cells
- if using multiple cells in a serial setup (e.g. 2 x 16340), use cells from the same production batch. Use and load them always together - as a pair
for life.
- do not leave them unattended when loading
- load them in an non-burning environment (I usually load them in my bathroom, non-flammable materials, somehow unattended while I am in another room but they won't set the house on fire when catching fire or exploding)
- load them in a vented environment (you do not want to breathe in the gases should they explode)
- don't overcharge them (should normally be prevented by the protection circuit as well as the charger, if using the right voltage and amperage)
- optionally, use a "Fireproof Explosion-proof Lipo Guard / Charge Protection Bag". I have one and sometimes use it.
- don't overdischarge them (should normally be prevented by the protection circuit)
- don't overload them regarding max. current draw. Should not be a problem with M61s (and should normally be prevented by the protection circuit anyway).
In short, quality cells and charger with M61s and a bit of common sense and pre-caution then the danger is very very small.
*)
E.g. Keeppower 16650 2500 mAh (nominal), with a "normal" charger charging the battery to 4.2 Volt, it has a (real) capacity of 1,900+ mAh:
https://lygte-info.dk/review/batteries2012/Keeppower 16650 2500mAh (Black) 2015 UK.html
(although the navigation is a little confuding this is a great site btw., has also reviews of chargers)