I just wanted to repeat something bildan stated:

THERE ARE MANY TYPES OF LITHIUM BATTERIES.

The term "Li-Ion" gets tossed around a lot, but it is incorrect to
call all Lithium batteries "Li-Ion", just like its incorrect to call
all sealed lead-acid batteries "Gel Cells" (ignoring the differences
between Gel, VRLA, and AGM).

There's the Li-Ion system/chemistry that is used in a lot of consumer
devices (such as what Brian tested). These tend to have a much better
track-record than many of the "Lithium Polymer" batteries (but at a
lower energy density). Some people use "Li-Po" and "Lithium Polymer"
interchangeably; while other groups use "Li-Po" to designate Lithium
Phosphate formulations.

And to make matters worse, "Li-Po" and "Lithium Polymer" batteries
themselves are now coming in different formulations. The earlier
"flat rectangle" cells from makers like Kokam were cutting edge for
awhile and used by many in the R/C modeling world; but have proven to
be highly flammable under high charge/discharge loads. One of the
telltale signs for these cells is that they provide 3.7 volts per cell
(a slightly awkward voltage for many applications).

Different Lithium formulations tend to provide slightly different
voltage on a per-cell basis. No particular per-cell voltage equates
to safety - but its a handy way to check what kind of cells you're
getting if the manufacturer isn't really specific about which brand or
formulation is being used inside the battery pack.

The LiFePo4 that is discussed in the Soaring magazine article is one
particular formulation. I haven't had a chance to research it in
detail, but it does look safer than some other "Li-Po" systems. If
the price comes down I'd certainly consider buying the new cells; but
as Brian pointed out the newer high-density SLA cells are pretty nice
for the price!

--Noel