[Elecraft] Windcamp X3 Li-ion Battery Box usage?

[Henry Pollock - K4TMC]

I keep seeing these on eBay.  They look neat with packaging that matches,
and attaches to, the KX3.  Looks like a good way to have an external
battery pack versus keeping batteries inside the KX3.  Wonder if anyone has
tried one of these?

Windcamp says to only use the 18650 batteries with a flat anode.  The only
ones that seem to meet that specification are the 3400mah NCR18650B variety
made for Panasonic.  There are other 18650 batteries available with higher
capacity (5000+mah), but they have the smaller rounded anode like normal AA
batteries.  Any thoughts on this?

73,

Henry - K4TMC

K3+/100, K2/100, KX3