They can be if you store them in something like an ammo box.  If they "go off" in the sealed box the pressure builds,  the reaction rate increases exponentially,  and voila... shrapnel time.  There's a video out there showing the results.

Most people recommend storing them in nomex/kevlar "cell bags".  I keep mine, bagged,  in an unused/unplugged oven!  If one goes off,  hopefully the flames won't spread to the rest of the property and the hinged oven door allows pressure to escape.

Hobby RC packs are one of the most dangerous type of rechargeable lithium cells out there... even from "reputable" sources and brands.  A local hobby shop twice had  brand new name brand packs sitting on the shelf go off.  A friend of mine had the same thing happen carrying a just purchased pack home in his car.

Whatever makes you feel safe, Mark. The internet has a plenitude of horror
stories, some of which would make you think that the only prudent course
was to store them in an underground bunker.

Our study used several hundred batteries, all stored in surplus cal .50
ammunition cases in manufacturers' packaging. We had no explosions, no
fires, no spontaneous combustions, no drama at all.

But do what makes you feel safe, by all means.

On Sunday, January 22, 2017, Mark Sims holrum@hotmail.com wrote:

--
If you gaze long into an abyss, your coffee will get cold.

Those hobby packs are typically LiPO, chosen for the energy density, and
they often (usually?) run them with minimal protection circuits to
reduce weight. Not recommended practice for building devices.

BMS
When I built a 12 cell series 10Ah pack, I went with LiFePO4 and a
custom-configured Battery Management System (BMS). The BMS doesn't
balance the charge after charging (which consumes time & energy), but
runs a separate lead to each junction between cells so it can monitor
each cell to vary each cell's charging to bring each to cell Vmax
without going over. Those leads also allow each cell to be monitored
against under voltage (cell Vmin). The cheap alternate is to rely upon
monitoring pack Vmax and pack Vmin protection, but this is a recipe for
killing a cell, as a cell may go over or under voltage while the pack
voltage appears within the safe range.

The LiFePO4 cell I chose is interesting for its self-containment.
Headway 38120, which was recommended as the cell is built encased within
a containment shell with a threaded terminal on each end. The negative
end's terminal is entirely sealed. The positive end's terminal is also
sealed, but there are air holes spaced around the cap-to-container join
and the true seal is an inner cap under that terminal cap (visible
through those holes). When the cell fails, rather than pressure causing
a leak, the inner sealing cap can expand into the space under the
terminal cap thereby relieving a critical level of pressure. Or so it's
claimed; I've never had an incident to test that.

Michael

On 22/01/2017 9:25 PM, Mark Sims wrote:

No way will an ammo box explode and send shrapnel flying.  Even if filled
with machine gun bullets and tossed in a fire.  The rubber gasket fails and
the pressure escapes.  A slow burning object like a battery will never
cause steel to fragment.  If someone made a video it was faked

The purpose of the box is that first it offers mechanical protection in
storage and transport and second it is a heat sink.  If a few hundred watts
of energy is put into a small part of the box, the heat conducts to a
larger area and you have a lower temperature.

The box is designed to store ammo in a combat area, the box will not
explode if something inside of it catches fire.  The gasket would fail
first or it not the wire bail holding the lid would fail under minimal
pressure.  The lid opens LONG before the steel can bursts

If I wanted to make a dramatic video, I'd fill the entire box with gun
powder.  The lid would fly open and burning powder would to ejected into
the air and it would LOOK like an explosion

On Sun, Jan 22, 2017 at 6:25 PM, Mark Sims holrum@hotmail.com wrote:

--

Chris Albertson
Redondo Beach, California

Hi Mark:

I agree.
The Vietnam era PRC-25 radio had a solid metal battery box that was water tight and used a BA-4386 battery with
Magnesium chemistry.
http://www.prc68.com/I/PRC25.shtml#DCP
The problem was that as a normal part of its operation the battery releases hydrogen gas.  I know someone who has a scar
on his head because when he opened the battery box the pressure shot it into his face.  No chemical explosion, just gas
pressure.

The more modern radios that use the BA-5590 (BA is military speak for primary) Li-SO4 battery where the sulfur is
compressed to make it a liquid have been known to explode if you try to charge them. This has resulted in a requirement
for all battery boxes/spaces to allow for one cell to "vent" and not cause a problem.  This is even more important with
the current BB-2590 (secondary/rechargeable) battery made up of a couple dozen 18650 Li cells.
http://www.prc68.com/I/BA5590.shtml#BB-2590Inside

PS This "5590" family of batteries are all form-fit-function interchangeable and are made up of two "12 Volt" batteries
in one 5.0 x 4.4 x 2.45" box.  It's the standard battery in the military for non vehicle applications that need vehicle
compatibility (ie either 12 or 24 volts).  The radio or host device can wire its plug so the battery appears as either a
12 or 24 volt battery.  While the long in the tooth BA-5590 can only supply a couple of amps (internal fuse) the newer
BB-2590 can supply maybe 35 Amps for a short time, I think to start a motor.

Rather that buying raw 18650 cells and connecting them getting a BB-2590 may be a better option.  There are numerous
military chargers that can charge them as well as hobby grade chargers that work with Li cells.

There are some very low cost battery capacity testers on eBay:
http://www.prc68.com/I/BatTst.shtml#Resistor - good for 18650 cell testing

http://www.prc68.com/I/BatTst.shtml#EL - good for BB-2590 testing

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

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