If you want to know everything about aircraft electrical systems have a look at;
http://www.aeroelectric.com/
Lots of battery stuff. Advice is charge a flat battery for 4 – 6 hours before relying on it to be voltage stable under load. This does not change no mater how good the alternators! You will also find a very good article on the difficulties of testing the “capacity” of a partly discharged battery, including some practical ways of doing this (in VMC).
Rod1