[Elecraft] RE; How well does the K3 work with lower power supply voltage . . .

[Charlie T]

When I worked for Vectrol Inc, we designed a new production, battery forming
charger which is needed to make new lead-acid batteries, so I learned a
little about your typical "car" battery when talking to the engineers.
Granted, this was over 40 years ago, so battery technology has obviously
changed a lot since then.
Basically, a pure chemical lead/acid battery cannot supply the yuge starting
current required to crank over a big V8 engine, so antimony is added to the
plates which drastically increases the max current rating.
However, the down side is that this chemical composition battery is
irrevocably damaged if it is allowed to discharge below a certain voltage.
"Deep-Cycle" batteries are simply regular lead/acid batteries without the
added antimony, thus allowing recoverable discharge way below that which
would kill a "car" battery.  They won't crank your muscle car over, but a
small electric outboard boat motor is fine. 

Since the IMD degrades at low DC supply voltages in our typical 12V powered
finals, if you must use a deep-cycle lead/acid battery,  I suggest using one
of those battery booster things that MFJ and probably others sell to keep
the output up.

73, Charlie k3ICH