How to charge a spare car battery at home and in the car?

Situation: I want to add another car battery to power my electronics in my car.





Question:


1. How do I charge it to full capacity at home?


2. How should I wire the battery so the car will charge my battery when the car is on?


3. Can I use a voltmeter to measure the capacity of the battery?|||Would suggest you try to stop by or call your nearest Batteries Plus store ( http://www.batteriesplus.com ).





They always were able to help me when I've add odd battery questions