[Elecraft] Does this look like a low battery problem?

[J Chester]

Hi,

Out portable yesterday - KX3 powered by an 8400mahr LiFe battery pack, which was fully charged that morning before I started operations. Antenna was a Buddipole vertical on 7119, SWR1.1, with j, C and L components all zero (ie on the antenna's resonant frequency). KX3 running at 15W out.

After an hour of operating (SSB), the KX3 started to wander off frequency by a 1Khz on transmit. A contact noticed this during a QSO. The battery showed 13.1v at the time.

I changed the battery, and with the new one the KX3 worked normally.

Is this a low battery issue, or do I need to look elsewhere?

Thanks

Joe
MW1MWD