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

[inventor61 .]

I have recently received the LiFePO4 battery pack I ordered for the K2 and
which I mentioned in an earlier posting.

Upon receipt I checked it out mechanically.  It looks very nicely made.
The supplied pigtail is terminated with the mating internal K2 Molex DC
connector.

I charged the new pack using a precision lab type CC/CV power source and it
accepted a full charge, according to my expectations.  After 48 hours, the
pack, with no load applied, dropped about 0.6V also as expected.

I did not yet try to install the new pack in the K2 but the micrometer says
that it will perfectly fit the Elecraft KBT2 bracket for which the new pack
was purposefully designed.

This pack *is *equipped with a protection card, limiting short circuit
current, over voltage, and under-voltage (low voltage disconnect); the
latter is to prevent ruining the pack by leaving it across a load.

The pack does *not* have a balancer built in.

I recognize the possibility that this can reduce the ultimate pack capacity
over time, but I have also looked into the matter in some depth (and I have
a background commercially in both primary and secondary cell / pack design
trade-offs).  I feel comfortable with my decision to not equip this pack
with a balancer, which among other things would have made the physical
dimensions of the pack not match what was needed in this radio.

The pack cannot be charged correctly (in most all states of discharge)
using a conventional constant-voltage external power supply on the K2.
Instead, after I retire the SLA, I will use a CC/CV type charger intended
for the purpose.  Further, the LiFePO4 pack should not be floated
indefinitely in CV mode.

The primary challenge I see with the setup as it is shipped from
Batteryspace is that the pack's stock cabling is not configured for for the
KBT2 battery disconnect switch to be placed in series with the pack.  This
switch would allow me to operate the K2 from a conventional power source
such as the Pro Audio Engineering PAE-KX33 unit.

To get around this problem, I will use suitable connectors and arrange for
the KBT2 power switch to be inserted in the (+) lead between the new pack
and its Molex fitting.  I will also inform the very helpful gentleman at
Batteryspace about a good way to redesign his pigtail to make this work for
other people.

I do not wish to (and will not) add a separate battery charge jack on the
radio.

The advantages of the SLA are that it is rather robust, can float charge
from the typical power source, and is relatively inexpensive.

Weight may or may not be an advantage.  The SLA certainly gives the K2 some
heft and a solid feel.  But it's not light and portable use often requires
lugging the radio about.

The advantages of the LiFePO4 pack are significantly longer run time from a
charge (I am thinking 2x), and an anticipated much longer service life.

I will report once more sometime in the future after I have suitable
real-world  experience using the new pack.   It may be some time before I
make this report; in relative terms however, it won't take too long since
I've been on this reflector daily for about 16 years.   ;-)

73  Steve KZ1X