[Elecraft] KX3 battery question again

[Chip Stratton]

I'll contribute my experience.

The ideal is probably the Buddipole A123 pack. These are a safe technology
(compared to LiPo) and for light duty use, which includes radios, it can be
charged at relatively low currents like a NiMh pack or SLA battery, i.e. by
applying 14 volts with current limiting to to a 4S pack). Optimally they
should be charged by a cell balancing charger like the Cellpro Multi4 - at
least every few cycles, but with good voltage and current limiting (at an
amp rate of no more than 1/10 of their capacity) I have found they can be
charged in series, and they tolerate a bit of a low current overcharge with
no problems (unlike LiPo) and the cells will generally stay in balance when
used and charged this way - if the cells are of high quality to begin with.
They will also last more years than LiPo, which you can expect to be end of
life after 3 or 4 years even if well taken care of.

You can find LiFePO4 packs from other vendors for a lot less, BUT it might
be a gamble. I've purchased a number of them from Hobbyking because they
are relatively very cheap, but at least half of them came to me with one
very weak cell in the pack. This makes them not quite so cheap. I did buy a
2300 mAh LiFePO4 pack on Ebay from a vendor for a very good price that is
holding up very well. It claims to be made with A123 brand cells though I
would be surprised. Nevertheless it lives and charges in my K2 in place of
the original SLA battery and has done very well.

If you are willing to invest in a cell balancing charger, a LiPo pack will
be a good choice. They have a better power/weight ratio than the LiFePO4
packs and are usually a lot cheaper than them for a given capacity, but
they are much more demanding about proper charging and careful handling.
Abused they can catch fire and/or vent very noxious gases at high
temperature. I've shot  an end of life LiPo pack with a pellet gun, and it
made quite a display! You must balance charge them, they absolutely  should
not be series charged like you can do with Nimh and SLA and with
limitations LiFePO4.

LiPo and LiFePO4 are very nice because they hold their charge with little
self-discharge. Once charged, they can sit for a long time and still be
ready to go with nearly full capacity, unlike typical Nimh or lead acid
technology. Sanyo Eneloops hold their charge much better than standard Nimh
cells, but do still self-discharge.

You might look into getting a 10 cell AA battery holder and fill it with
good Nimh cells like Sanyo Eneloops. Very safe, good capacity, easy to
maintain. You can series and trickle charge the pack with a proper charger
and maintain cell balance that way. Or you can charge cells individually,
which is still the ideal. Downside is that there are 20 battery contacts in
that holder and over time connections between cells may become dodgy.
Probably the best solution if you don't want to get adventurous.

Chip
AE5KA