yeah, wire the batteries in series, so the neg of one goes to the pos of the next and then complete the circut. You want 18 volts to be going through the board, not 9 (that will cause the battery light to stay on).
All you are doing is swapping the connections, so no it won't make the batteries last longer, speed up your hopper, make you harder to hit etc
It stops the batteries from putting so much pressure on the lid catches, so your shells last longer. And continues to give a connection even if the battery lid does spring open.
All it does is make your bank account automatically replenish itself as you sleep, this makes you more attractive to women. It also means you have the money to buy your own supa'air field with really huge bunkers so you feel really little next to them and their is no gaps between them on a normal sized millenium field so you make the 50 everytime and feel that you're only doing this because your faster than you were yesterday.
Its easy to see where this misconception comes from