The manual for the KX2's internal battery charger (KXIBC2) allows for a variety of input voltages, up to a maximum of 15V, to be used to charge the radio's 2.6AH lithium battery. The manual also mentions that lower voltages (down to 11V) can also be used although the battery will not be fully charged at these voltages.

I was curious to see how a lower charging voltage - ie, a partial charge - would correspond to capacity.

My main interests were:

• If I charge the KX2's battery from my motorcycle's lead-acid battery, how much capacity will it have?
• If I charge a completely discharged KX2 battery from the motorcycle, will I still have enough juice in the motorcycle battery to be able to start the bike?

The following chart shows the resulting capacity of the KX2's battery when charged from various voltage sources. And the bike started right up :-)

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As I prepare to hit the 'Publish' button on this posting, a new product has just been announced.

Manuel HB9DQM has developed a non-Elecraft internal battery charger for the KX2. He calls it the KXUSBC2 and it allows the KX2's battery to be charged via a USB-C port.

Interestingly, the USB-C port is bidirectional and can therefore be used to charge a smartphone or other USB-C device from the KX2's battery if necessary.

More information and photos of the KXUSBC2 are here.

The thread of the announcement and Elecraft's response is here. 

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