As is so often the case, this is one more idea a day late and a dollar
short. The product aleady exists. Just check out the world of radio
controlled models. These folks live and die with their nicads. There are
many products to help them charge their batteries and keep them that way. At
least one company makes a tester that
        a) charges a nicad pack
        b) then discharges it
        c) then charges it
        d) then reports the total amp-hours of capacity.

When you are launching an rc glider for a 2 hour flight, it's important to
know you are going to get enough juice to complete the flight without crashing.

Happy New Year!
Tom Messenger