Personally, what I would do is make my own BMS. I designed a simple one back when I had my enginer kit in my Prius. It is based off an arduino and using a few celllogs which measure cell voltages. The charging side worked great, I never finished the discharging side of it. However, a simple amp hour counter gauge would work fine, just not be automated, you could switch it off once you use 7-8Ah.
Here is the link where I had worked on it:
http://ecomodder.com/forum/showthrea...tem-20445.html