Soon afterwards I learned of another battery with the same specs: 2600 mAH, protection circuitry and small enough to fit in the KX2 - and, at $25, it was $8 less expensive than the first one.
These batteries have both changed in price since I ordered them and both are sold via eBay with free shipping.
And while both have about the same capacity, the discharge curve of one battery occurs at a higher voltage than the other. This may be due to the protection circuitry characteristics rather than on the battery cells themselves.
For those interested, here are the curves and links to each battery.
Red curve battery (now down to $22 with free shipping)
Green curve battery (also $22, free shipping)
|Discharged at a 100 mA rate|