[Elecraft] KX1 on AAAs or Lithium Polymer?

[K. Rice]

My experiences are with K1, not KX1 but may generalize if I can
manage to keep the form factor in mind.  Also I use 18650 Li-Ion
cells but use figures for 14500 cells below, as 18650s are too
big for this application.

As others have mentioned, these cells require a specialized
charge-discharge regime. For that reason I don't put Li-Ion 
cells inside radios, but I might if Wayne designed the charge 
controller.  :)

For the KX-1, 14500 series (AA-size) cylindrical Li-Ion cells should
work nicely in 3S2P configuration with a protection IC/PCB for 
each of the two AA-size 3-packs to prevent overcharge/overdischarge 
and non-uniform charge distribution across cells. (As others have
mentioned, the latter is a problem with Li-Ion cells that can 
lead to catastrophic failure).

3S2P configuration gives 11.1 volt nominal at 1500 mAh.  Peak 
voltage is 12.3-12.6 volts depending on how they're charged, 
and it stays above 11.1 volts for a good long time ... 3 hours, 
say, with casual operating.  The IC/PCB sheds the load when 
per-cell voltage drops to 2V, insuring long life and long-term
rechargeability.
 
Weight is around 4.8 oz and the new pack wouldn't require more
and hence smaller cells (e.g. AAA-size) than the original design,
presumably reducing the cost of a redesign.

Cost is about 1/2 of equivalent Li-poly.  Li-poly saves a little 
over 2 oz in weight, but some of the saving will be offset by 
the need for additional packaging to protect the fragile poly 
flat-pack.

I fuse my pack at 2A and keep it in a plastic project box with
a panel-mount PowerPole connector.

I get this stuff from batteryspace.com - usual disclaimer applies.

73
Ken K3VV