You wont notice the difference. If you look at it like water. You have a gallon and use 1/2. You still need to refill 1/2. An advantage to dual batteries is if one fails, you have another still. The reality is, if one fail's most people don't know how to test it or deal with it and its easier to deal with a single than two or more. The more you have, the more complex. I personally prefer to just deal with one. Sometimes two is preferable or necessary.