[Elecraft] [K2] LiFePO4 replacement for internal SLA battery in K2

[inventor61 .]

I had strongly considered the LiPo type secondary-cell power packaging
option and rejected it.

Energy density in that chemistry/package is amazing of course.  But that
equation is also true of a bomb.  I have no problem with the LiPo in my
iPad, Galaxy S5 phone, and laptop, so, it's not a blind bias.

It doesn't take too much YouTube searching to find dramatic examples of
LiPo powered RC vehicles and the like bursting into flames.

There's a good reason that *all* these lithium cells are considered hazmat
now, not just the lithium thionyl chloride ones ... on failure, those burn
and emit nerve gas; they are Class 9 hazmat!  They are also not
rechargeable anyway.

Because this particular power pack would be fully enclosed in the
metal-cased K2, and would be in the 9 ampere-hour range in this desired
form factor ... if such a LiPo pack decided to self-immolate, the rig would
not only be destroyed but I'd have a real secondary incendiary hazard on my
hands.

The charging, power regulation and protective circuitry, etc., needed to
use the LiPo chemistry/packaging inside a K2 took that consideration off
the table for me.  YMMV.

The 'safe-failure-mode' secondary-cell chemistries I considered were NiMH
and LiFePO4.

The NiMH almost won.

By the way, I have the special spot-welder device and strap/bracket
supplies needed to fabricate my own packs.  Extensive experimenting with
NiMH cells really had me convinced to go that way for some time.

Then, I got some newer LiFePO4 cells and also some new LiCoO2 cells, and
started the "2015 edition" revisiting of the selection analysis.  I had
last looked at the issue in 2010.

It didn't take long before my own clumsiness lit one of the 18650-size
LiCoO2 cells up.  I caught the mistake just as it was about to get really
serious.  Lesson learned.  Now I know why the manufacturers of those
include the built-in-per-cell safety circuit option!  The cells I tried
were the 'raw' and unprotected type, selected purposefully so as to not
have the size, cost, and loss of the protective circuitry.  For these and
other reasons, this chemistry/packaging option was rejected for the
particular use-case.

I could not achieve a better-than-the-SLA result with NiMH.

Hope my describing a portion of the ferreting process in a bit more depth
is of use to others.

The K2 is a remarkably competent field radio.  Being able to actually use
it in the field, conveniently, makes my now-teenage rig all the more
valuable to me.  Having a modern internal power source will just be icing
on an already tasty cake.

73  Steve KZ1X