In my original post I mentioned that the Batnav unit draws its power from an Anabat SD2's USB socket. This was incorrect - it actually draws power from the serial port. They have also now launched an SD1 version (similar to the one I tested) with a power connector which clips into the battery case.
The Batnav was designed to be used with an Anabat SD2 and comes with the GPS receiver and KML generator software. Bob advises they are now developing an upgraded version of the Batnav KML generator, which they plan to sell as a stand-alone product for people using other GPS receivers or ZCA bat detectors, which is good news.
My other niggle was that the Batnav's magnet was insufficient to get it to stick to an Anabat cover (as advertised). This was fine for vehicle transects, as the Batnav stuck well to the exterior of the car, but more of a problem for walked transects. Wildwood have sourced an adhesive ferrous strip (which is oddly rustproof), which can be stuck to the Anabat, to give the Batnav something better to stick to than the Anabat case. This improves matters and allows you to stick the batnav to the rear of the Anabat instead of the front, though it may not get as good a GPS signal there. However, I find that the Batnav can still come adrift. With some experimentation I have found that the problem is actually the Batnav's slightly stiff cable, acting as a lever and forcing the Batnav's magnetic pad off the Anabat. Coiling up the excess cable round the serial plug with a cable tie has reduced the problem significantly. An alternative would be to use a stick-on cable grip (from any DIY store) on the Anabat, to stop the Batnav cable moving around.
The Batnav website: www.batnav.com