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

JDjoduJD: 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?

Answers and Views:

Answer by Frank B
Would suggest you try to stop by or call your nearest Batteries Plus store ( https://www.batteriesplus.com ).

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