1) Using unprotected cells.
2) Using 2 different batches of unprotected cells (note label style markings).
3) Charging Li-Ion in series without balance taps is not safe--especially with unprotected cells. When I finally removed battery holder from light, and took this exact FM battery holder apart to check voltages after charging it about 10-15 times, the highest and lowest voltage cells were far apart. So the highest voltage cell was in the process of being increasingly overcharged.
4) Wrong cell number selected with slider switch on what I now call my "Old Oxymoronic Charger." ("Universal Smart" is the oxymoron...akin to "Military Intelligence")
5) Bad quality cheap Chinese charger....no reliable termination, uses cell number in series to figure total voltage, selected by switch and charges to that. First charger shorted while charging, I smelled smoke in other room, noticed charger plastic was significantly melted and deformed. Almost impossible to read which cell number voltage you are choosing, and no distinct "click" to confirm slot to slot.
6) First charging plug shorted out and melted plastic as apparently I had too much solder that made contact as I screwed plastic shield down. Happened when first plugged into FM tailcap setup with 4 Li-Ion cells. I threw first, melted one away, and soldered another one that you see shown in photo.
7) No reliable Red/Black wire to confirm polarity coming out of plug.
8) Bare wires make it easy to short against clip lead, battery holder metal contacts.
9) Tightening this style of battery holder can press center post through plastic & cause dead short. It happened to me early on.
10) Charging on highly flammable surface.
11) Charging in obvious living space. I would watch TV while it was charging on couch or wood coffee table. My strategy was to keep it within eyeshot to see when indicator light turned green.
12) No fire protection tools or strategy if there was a fire. This was a reflection of my having no awareness of the dangers of Li-Ion charging.
13) No DMM to verify voltages.
I later "sprung" for a $20 Rat Shack yellow DMM, that would not work properly when battery began to wear out. Did not see the advertised low battery warning display. Alkaline round 12V battery leaked inside, so perhaps there was a bad contact issue.
14) Normally all the charging was done with cell pack kept in light as FM designed it...which I believe is a mistake because you cannot see what is happening to the cells. I showed you the pack holder being charged outside the light in photo, but at least 15 charges were done through tailcap hole with pack never being removed from light.
15) No surge protector or "UPS" (Uninterruptable Power Supply) was used, and while charging during several lightning storms, power to our house/neighborhood was lost and spiked back on...at least twice.
16) No temp or total charge time monitoring was done as a backup in case I forgot about the charge. Once I forgot about charging and went to sleep. There it was on the couch in the morning.
Suffice it to say that I have since learned a few things about all this.
