6V charge controllers

I’m currently toying around with a stepper motor that I plan on using as a bike dynamo and a wind generator which will be hooked up to a 6 volt battery. The idea here being to have a modular design so that I can charge a 6 volt battery at lower rpms if I had the need to and wire 2 6 volt batteries in series to get a 12 volt battery.

My problem is that there doesn’t seem to be a lot of choices when it comes to using a 6 volt charge controller, I’ve only found one that seemed adequate from googling .

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=251215109574&var=550262128346&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en

Another option would be using the LM2596 chip sold on ebay but I’ve no idea as to how well that would work.

Thoughts?