[Ross Nicol]

Tom - Thanks for your input, made me put in a lot of research into the matter, and uncovered answers to a lot of my grey areas with batteries and charging.I'm sure we have all grabbed a battery charger and used it to charge a flat battery without thinking about the technical aspects of what is happening.
The Batteries internal resistance is very low as you say and just like all power sources it causes a voltage drop at the output (bat terminals) when current flows. In a car the most dramatic example is when you crank the starter motor.The internal battery resistance small as it is (.01 ohms or similar) becomes significant when the starter draws a few hundred amps.
When the motor is running current flows into the battery (as long as you haven't turned all the accessories on).It is constant voltage charging as the Alternator output is regulated to approx 14.5volts.Now my problem with understanding this setup was 'what limits the current?' as the internal resistance is so low it cannot play a part.The answer is 'back emf' initially the flat battery with low back emf allows max current to flow into the battery but as it charges up the back emf rises to a point where a fully charged battery recieves very little current.This explanation is very hard to find in books.An ammeter displays the current reduction very well.
I hope you agree with me now Tom.

Malc
I came across an interesting article about different batteries requiring different regulated voltages for full charging.Optima was mentioned.What this means is, as you have done, ask the battery manufacturer what the alternater's regulated voltage needs to be.The ramifications of not matching battery and alternator can force you to externally recharge it and short battery life due to sulphating.

I hope others get something out of this,as far as I'm concerned I don't mind being wrong as long as I can learn from it.

Ross