[Elecraft] K3 real time clock - backup battery?

[David Ferrington]

>The K3 has a very versatile real-time-clock chip that runs when the rig
>is off. It draws about 3 microamps as I recall. If you have an alarm
>set, it will wake up the radio at the appointed time.

Is there some form of backup while its off the main power, like being
carried to a field location?

I'm reading the archives, having rejoined the reflector just to read about
and decide on a K3, so forgive me if I missed this.

K2 - 2nd highest mountain in the world (and a rig).
K3 - 1st radio that is out of this world.
- 
There are three truths: my truth, your truth, and the truth.
-Chinese proverb